Income Taxes Income Taxes (Schedule of Effective Income Tax Rate Reconciliation) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Statutory U.S. federal tax expense									$ 413	$ 340	$ 527
Valuation allowance change, excluding expirations									(219)	(8)	(49)
State and local income taxes, net of federal income tax benefit									50	26	7
Nondeductible expenses									29	28	4
Tax credits, excluding expirations									(27)	(20)	(12)
Changes in unrecognized tax expenses (benefits)									5	22	1
Change in enacted tax rate, amount									(1)	(23)	119
Other tax adjustments, net									(4)	(6)	(16)
Income tax expense from continuing operations	$ 106	$ 119	$ (90)	$ 111	$ 79	$ 91	$ 113	$ 76	$ 246	$ 359	$ 581
Federal statutory income tax rate									21.00%	0.00%	35.00%