Other Comprehensive Income (Accumulated Other Comprehensive Income (Loss) Components) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net Unrealized Gains Losses on Non Otti Securities [Abstract]
Net unrealized gains (losses) on non-OTTI securities, after-tax, Beginning Balance	$ 52	$ 286	$ 647
Other Comprehensive Income (Loss), Non Otti Securities Adjustment, After Tax	10	(234)	(361)
Net unrealized gains (losses) on non-OTTI securities, after-tax, Ending Balance	62	52	286
Net Unrealized Gains Losses On Otti Securities [Abstract]
Net unrealized gains (losses) on OTTI securities, after tax, Beginning Balance	106	66	74
Other Comprehensive Income Loss Otti Securities Adjustment After Tax	109	40	(8)
Net unrealized gains (losses) on OTTI securities, after tax, Ending Balance	215	106	66
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax [Abstract]
Net unrealized gains (losses) on cash flow hedge derivatives, after-tax, Beginning balance	333	430	350
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	(182)	(97)	80
Net unrealized gains (losses) on cash flow hedge derivatives, after-tax, Ending balance	151	333	430
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, before Tax [Abstract]
Pension and other postretirement benefit plan adjustments, after tax, Beginning Balance	(553)	(554)	(520)
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	107	1	(34)
Pension and other postretirement benefit plan adjustments, after tax, Ending Balance	(446)	(553)	(554)
Other Comprehensive Income Other Adjustments [Abstract]
Other, after tax, Beginning balance	(203)	(98)	(48)
Total Other, net activity, After tax	73	(105)	(50)
Other, after tax, Ending balance	(130)	(203)	(98)
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning Balance	(265)	130	503
Other comprehensive income (loss), after tax and net of reclassifications into Net income	117	(395)	(373)
Accumulated Other Comprehensive Income (Loss), Net of Tax, Ending Balance	$ (148)	$ (265)	$ 130