Private Equity Investments Real Estate Funds Insurance Deposits Contracts Retirement Annuity Contracts Total  Level 3 Assets December 31, 2018 $ 20  $ 68  $ 128  $ —  $ 216  Actual return on plan assets: Unrealized gains, net 5  6  6  —  17  Purchases, sales and settlements, net 1  10  3  35  49  December 31, 2019 26  84  137  35  282  Actual return on plan assets: Unrealized gains, net 5  7  18  3  33  Realized losses, net —  (1) —  —  (1) Purchases, sales and settlements, net 2  —  2  —  4  December 31, 2020 $ 33  $ 90  $ 157  $ 38  $ 318  Changes in our Level 3 defined benefit plan assets during 2020 and 2019 were as follows: We have four operating segments: Aerospace, Marine Systems, Combat Systems and Technologies. We organize our segments in accordance with the nature of products and services offered. We measure each segment’s profitability based on operating earnings. As a result, we do not allocate net interest, other income and expense items, and income taxes to our segments. Summary financial information for each of our segments follows: S. SEGMENT INFORMATION Corporate operating results consist primarily of equity-based compensation expense. Corporate operating results in 2018 also included one-time charges of approximately $45 associated with the costs to complete the CSRA acquisition. * See Note B for additional revenue information by segment. 96 Revenue* Operating Earnings Revenue from U.S. Government Year Ended December 31 2020 2019 2018 2020 2019 2018 2020 2019 2018 Aerospace $ 8,075  $ 9,801 $ 8,455  $ 1,083  $ 1,532 $ 1,490  $ 513  $ 498 $ 334  Marine Systems 9,979  9,183  8,502  854  785  761  9,871  9,027  8,245  Combat Systems 7,223  7,007  6,241  1,041  996  962  4,191  4,048  3,228  Technologies 12,648  13,359  12,995  1,211  1,311  1,267  11,728  12,234  11,799  Corporate —  —  —  (56) (54) (86) —  —  —  Total $ 37,925  $ 39,350 $ 36,193  $ 4,133  $ 4,570 $ 4,394  $ 26,303  $ 25,807 $ 23,606 