Accumulated Other Comprehensive Income Reclassifications out of AOCI (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax		$ (1)	$ 108	$ (4)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax		0	(40)	1
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax		(1)	68	(3)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax		72	(89)	(244)
Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, Tax		(17)	33	91
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax		55	(56)	(153)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, before Tax		(6)	(6)	(6)
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss), Net Actuarial Gain (Loss), Before Tax		22	25	(25)
Deferred losses related to NCF Retirement Plan settlement	[1]	60	0	0
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax		76	19	19
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax		(18)	(6)	(7)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, after Tax		58	13	12
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		$ 112	$ 25	$ (144)

[1] Related to the Company's NCF Retirement Plan settlement in the fourth quarter of 2018. See Note 17, "Employee Benefit Plans," for additional information.