Other Comprehensive Income (Accumulated Other Comprehensive Income (Loss) Components) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of ASU adoptions	[1]		$ (16)
Net Unrealized Gains Losses on Non Otti Securities [Abstract]
Net unrealized gains (losses) on non-OTTI securities, after-tax, Beginning Balance		$ 62	52	$ 286
Other Comprehensive Income (Loss), Non Otti Securities Adjustment, After Tax		(405)	10	(234)
Net unrealized gains (losses) on non-OTTI securities, after-tax, Ending Balance		(284)	62	52
Net Unrealized Gains Losses On Otti Securities [Abstract]
Net unrealized gains (losses) on OTTI securities, after tax, Beginning Balance		(215)	(106)	(66)
Other Comprehensive Income Loss Otti Securities Adjustment After Tax		(11)	109	40
Net unrealized gains (losses) on OTTI securities, after tax, Ending Balance		(204)	(215)	(106)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification, before Tax [Abstract]
Net unrealized gains (losses) on cash flow hedge derivatives, after-tax, Beginning balance		151	333	430
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax			(182)	(97)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax		(137)
Net unrealized gains (losses) on cash flow hedge derivatives, after-tax, Ending balance		47	151	333
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, before Tax [Abstract]
Pension and other postretirement benefit plan adjustments, after tax, Beginning Balance		446	553	554
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax		12	107	1
Pension and other postretirement benefit plan adjustments, after tax, Ending Balance		530	446	553
Other Comprehensive Income Other Adjustments [Abstract]
Other, after tax, Beginning balance		(130)	(203)	(98)
Total Other, net activity, After tax		(42)	73	(105)
Other, after tax, Ending balance		(162)	(130)	(203)
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning Balance		(148)	(265)	130
Other comprehensive income (loss), after tax and net of reclassifications into Net income		(583)	117	(395)
Accumulated Other Comprehensive Income (Loss), Net of Tax, Ending Balance		(725)	(148)	(265)
Total
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of ASU adoptions	[1]		6
Other Comprehensive Income Other Adjustments [Abstract]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning Balance		(148)	(265)	130
Other comprehensive income (loss), after tax and net of reclassifications into Net income		(583)	117	(395)
Accumulated Other Comprehensive Income (Loss), Net of Tax, Ending Balance		$ (725)	(148)	$ (265)
Accounting Standards Update 2018-02 | Net unrealized gains (losses) on non-OTTI securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of ASU adoptions			59
Accounting Standards Update 2018-02 | Net unrealized gains (losses) on cash flow hedge derivatives
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of ASU adoptions			33
Accounting Standards Update 2018-02 | Pension and other postretirement benefit plan adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of ASU adoptions			(96)
Accounting Standards Update 2018-02 | Other
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of ASU adoptions			10
Accounting Standards Update 2018-02 | Total
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of ASU adoptions			$ 6

[1] Represents the cumulative effect of adopting ASU 2014-09, ASU 2016-01, ASU 2017-12 and ASU 2018-02. See Recently Adopted Accounting Standards portion of Note 1 Accounting Policies for additional detail on the adoption of these ASUs.