Total Equity and Other Comprehensive Income (Accumulated Other Comprehensive Income (Loss) Components) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Jan. 01, 2020	Jan. 01, 2019
Net Unrealized Gains Losses on Non Otti Securities [Abstract]
Other comprehensive income (loss), non otti securities adjustment, after tax		$ 492
Net Unrealized Gains Losses On Otti Securities [Abstract]
Other comprehensive income loss otti securities adjustment after tax		7
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification, before Tax [Abstract]
Other comprehensive income (loss), cash flow hedge, gain (loss), after reclassification and tax	605	77
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, before Tax [Abstract]
Pension and other postretirement benefit plan adjustments, net activity, After Tax	9	112
Other Comprehensive Income Other Adjustments [Abstract]
Total other, net activity, after tax	(36)	32
Other Comprehensive Income (Loss) Total [Abstract]
Accumulated other comprehensive income (loss), net of tax, beginning balance	799
Cumulative effect of new accounting principle in period of adoption			$ (671)	$ 62
Other comprehensive income (loss), after tax and net of reclassifications into Net income	1,719	720
Accumulated other comprehensive income (loss), net of tax, ending balance	2,518
Net unrealized gains (losses) on non-OTTI securities [Member]
Net Unrealized Gains Losses on Non Otti Securities [Abstract]
Net unrealized gains (losses) on non-OTTI securities, after-tax, Beginning Balance	844	(284)
Other comprehensive income (loss), non otti securities adjustment, after tax	1,146	492
Net unrealized gains (losses) on non-OTTI securities, after-tax, Ending Balance	2,213	208
Other Comprehensive Income (Loss) Total [Abstract]
Cumulative effect of new accounting principle in period of adoption			223
Net unrealized gains (losses) on OTTI securities [Member]
Net Unrealized Gains Losses On Otti Securities [Abstract]
Net unrealized gains (losses) on OTTI securities, after tax, Beginning Balance	223	204
Other comprehensive income loss otti securities adjustment after tax	(5)	7
Net unrealized gains (losses) on OTTI securities, after tax, Ending Balance	(5)	211
Other Comprehensive Income (Loss) Total [Abstract]
Cumulative effect of new accounting principle in period of adoption			(223)
Net unrealized gains (losses) on cash flow hedge derivatives [Member]
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	276	47
Other comprehensive income (loss), derivatives qualifying as hedges, net of tax	605	77
Net unrealized gains (losses) on cash flow hedge derivatives, after-tax, Ending balance	881	124
Pension and other postretirement benefit plan adjustments [Member]
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, before Tax [Abstract]
Pension and other postretirement benefit plan adjustments, after tax, Beginning Balance	(408)	(530)
Pension and other postretirement benefit plan adjustments, net activity, After Tax	9	112
Pension and other postretirement benefit plan adjustments, after tax, Ending Balance	(399)	(418)
Other [Member]
Other Comprehensive Income Other Adjustments [Abstract]
Other, after tax, Beginning balance	(136)	(162)
Total other, net activity, after tax	(36)	32
Other, after tax, Ending balance	(172)	(130)
Total [Member]
Other Comprehensive Income (Loss) Total [Abstract]
Accumulated other comprehensive income (loss), net of tax, beginning balance	799	(725)
Cumulative effect of new accounting principle in period of adoption			$ 0
Other comprehensive income (loss), after tax and net of reclassifications into Net income	1,719	720
Accumulated other comprehensive income (loss), net of tax, ending balance	$ 2,518	$ (5)