(a) This balance primarily represents regulatory liabilities for Excess ADIT as a result of the reduction in the corporate federal income tax rate from 35% to 21% related to the enactment of Tax Reform. The regulatory liability balance predominately pays a return due to the inclusion of Excess ADIT in rate base. (b) Relieved as removal costs are incurred. (c) Refunded using ARAM. APCo December 31, Remaining Refund Period Regulatory Liabilities: 2020 2019 (in millions) Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits Regulatory liabilities approved for payment: Regulatory Liabilities Currently Paying a Return Asset Removal Costs $ 678.9  $ 635.3  (b) Deferred Investment Tax Credits 0.3  0.5  33 years Total Regulatory Liabilities Currently Paying a Return 679.2  635.8  Regulatory Liabilities Currently Not Paying a Return 2017-2019 Virginia Triennial Revenue Provision 44.2  —  28 years PJM Transmission Enhancement Refund 16.3  19.5  5 years Virginia Transmission Rate Adjustment Clause —  28.1  Other Regulatory Liabilities Approved for Payment 12.3  18.0  various Total Regulatory Liabilities Currently Not Paying a Return 72.8  65.6  Income Tax Related Regulatory Liabilities (a) Excess ADIT Associated with Certain Depreciable Property 690.0  718.9  (c) Excess ADIT that is Not Subject to Rate Normalization Requirements 139.1  210.7  8 years Income Taxes Subject to Flow Through (356.4) (362.3) 24 years Total Income Tax Related Regulatory Liabilities 472.7  567.3  Total Regulatory Liabilities Approved for Payment 1,224.7  1,268.7  Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits $ 1,224.7  $ 1,268.7  273