Total Equity and Other Comprehensive Income (Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, before Tax [Abstract]
Net unrealized gains (losses) on securities, pre-tax	$ (1,181)	$ 1,662
Less: Net realized gains (losses) reclassified to earnings	13	182
Net increase (decrease), pre-tax	(1,194)	1,480
Other Comprehensive Income (Loss), Available-for-sale Securities, before Reclassification Adjustments, Tax [Abstract]
Net unrealized gains (losses) on securities, tax effect	278	(381)
Less: Net realized gains (losses) reclassified to earnings, tax effect	(3)	(42)
Effect of income taxes	281	(339)
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, After Reclassification Adjustments, after Tax [Abstract]
Net unrealized gains (losses) on securities, after tax	(903)	1,281
Less: Net realized gains (losses) reclassified to earnings, after tax	10	140
Net increase (decrease), after-tax	(913)	1,141
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification, before Tax [Abstract]
Net unrealized gains (losses) on cash flow hedges, pre-tax	(640)	830
Less: Net realized gains (losses) reclassified to earnings, pre-tax	135	45
Net increase (decrease), pre-tax	(775)	785
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification, Tax [Abstract]
Net unrealized gains (losses) on cash flow hedges, tax effect	151	(190)
Less: Net realized gains (losses) reclassified to earnings, tax effect	(32)	(10)
Effect of income taxes	183	(180)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax [Abstract]
Net unrealized gains (losses) on cash flow hedges, after tax	(489)	640
Less: Net realized gains (losses) reclassified to earnings, after tax	103	35
Net increase (decrease), after-tax	(592)	605
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), after Reclassification Adjustment, before Tax [Abstract]
Net pension and other postretirement benefit plan activity and other reclassified to earnings, pre-tax	30	12
Net increase (decrease), pre-tax	30	12
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax [Abstract]
Net pension and other postretirement benefit plan activity and other reclassified to earnings, tax effect	(7)	(3)
Effect of income taxes	(7)	(3)
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax [Abstract]
Net pension and other postretirement benefit plan activity and other reclassified to earnings, after-tax	23	9
Net increase (decrease), after-tax	23	9
Other Comprehensive Income Other Adjustments [Abstract]
Net unrealized gains (losses) on other transactions, pre-tax	1	8
Net increase (decrease), pre-tax	1	8
Net unrealized gains (losses) on other transactions, tax effect	1	(18)
Effect of income taxes	1	(18)
Net unrealized gains (losses) on other transactions, after tax	2	(10)
Net increase (decrease), after-tax	2	(10)
Other comprehensive income (loss), before tax and net of reclassifications into Net income	(1,938)	2,251
Total other comprehensive income (loss), tax effect	458	(532)
Other comprehensive income (loss), after tax and net of reclassifications into Net income	(1,480)	1,719
Continuing Operations
Other Comprehensive Income Other Adjustments [Abstract]
Net unrealized gains (losses) on other transactions, pre-tax	1	8
Other comprehensive income (loss), before tax and net of reclassifications into Net income	(1,938)	2,285
Total other comprehensive income (loss), tax effect	458	(540)
Other comprehensive income (loss), after tax and net of reclassifications into Net income	$ (1,480)	1,745
Discontinued Operations
Other Comprehensive Income Other Adjustments [Abstract]
Other comprehensive income (loss), before tax and net of reclassifications into Net income		(34)
Total other comprehensive income (loss), tax effect		8
Other comprehensive income (loss), after tax and net of reclassifications into Net income		$ (26)