Income Taxes (Schedule of Effective Income Tax Rate Reconciliation) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Statutory U.S. federal tax expense									$ 340	$ 527	$ 553
Nondeductible expenses									28	4	7
State and local income taxes, net of federal income tax benefit									26	7	35
Change in enacted tax rate, amount									(23)	119	0
Changes in unrecognized tax expenses (benefits)									22	1	(161)
Tax credits, excluding expirations									(20)	(12)	(15)
Valuation allowance change, excluding expirations									(8)	(49)	51
Other tax adjustments, net									(6)	(16)	0
Income tax expense from continuing operations	$ 79	$ 91	$ 113	$ 76	$ 231	$ 115	$ 122	$ 113	$ 359	$ 581	$ 470
Federal statutory income tax rate									21.00%	35.00%	35.00%