Income Taxes (Schedule of Effective Income Tax Rate Reconciliation) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Statutory U.S. federal tax expense									$ 297	$ 413	$ 340
Change in tax resulting from, Nondeductible Expenses									37	29	28
Change in tax resulting from State and Local Income Taxes, net of federal income tax benefit									36	50	26
Change in tax resulting from tax credits, excluding expirations									(29)	(27)	(20)
Change in tax resulting from changes in unrecognized tax benefits									4	5	22
Change in tax resulting from valuation allowance change, excluding expirations									(3)	(219)	(8)
Change in tax resulting from tax law enactment									0	(1)	(23)
Change in tax resulting from other, net									(14)	(4)	(6)
Income tax expense from continuing operations	$ 169	$ 156	$ 95	$ (92)	$ 106	$ 119	$ (90)	$ 111	$ 328	$ 246	$ 359