Total Equity and Other Comprehensive Income (Accumulated Other Comprehensive Income (Loss) Components) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption					$ (16)
Net Unrealized Gains Losses on Non Otti Securities [Abstract]
Net unrealized gains (losses) on non-OTTI securities, after-tax, Beginning Balance	$ (494)	$ 189	$ 121	$ 52
Other Comprehensive Income (Loss), Non Otti Securities Adjustment, After Tax	(251)	41	(866)	178
Net unrealized gains (losses) on non-OTTI securities, after-tax, Ending Balance	(745)	230	(745)	230
Net Unrealized Gains Losses On Otti Securities [Abstract]
Net unrealized gains (losses) on OTTI securities, after tax, Beginning Balance	227	166	215	106
Other Comprehensive Income Loss Otti Securities Adjustment After Tax	0	44	12	104
Net unrealized gains (losses) on OTTI securities, after tax, Ending Balance	227	210	227	210
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax [Abstract]
Net unrealized gains (losses) on cash flow hedge derivatives, after-tax, Beginning balance	(52)	278	184	333
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	(54)	(30)	(290)	(85)
Net unrealized gains (losses) on cash flow hedge derivatives, after-tax, Ending balance	(106)	248	(106)	248
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, before Tax [Abstract]
Pension and other postretirement benefit plan adjustments, after tax, Beginning Balance	(489)	(564)	(542)	(553)
Pension and other postretirement benefit plan adjustments, net activity, After Tax	1	7	54	(4)
Pension and other postretirement benefit plan adjustments, after tax, Ending Balance	(488)	(557)	(488)	(557)
Other Comprehensive Income Other Adjustments [Abstract]
Other, after tax, Beginning balance	(132)	(167)	(120)	(203)
Total Other, net activity, After tax	(16)	14	(28)	50
Other, after tax, Ending balance	(148)	(153)	(148)	(153)
Other Comprehensive Income (Loss) Total [Abstract]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning Balance	(940)	(98)	(148)	(265)
Other comprehensive income (loss), after tax and net of reclassifications into Net income	(320)	76	(1,118)	243
Accumulated Other Comprehensive Income (Loss), Net of Tax, Ending Balance	(1,260)	(22)	(1,260)	(22)
Accumulated Other Comprehensive Income (Loss), Net of Tax, Adjusted Balance					(142)
As Previously Reported [Member]
Net Unrealized Gains Losses on Non Otti Securities [Abstract]
Net unrealized gains (losses) on non-OTTI securities, after-tax, Beginning Balance			62
Net Unrealized Gains Losses On Otti Securities [Abstract]
Net unrealized gains (losses) on OTTI securities, after tax, Beginning Balance			215
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax [Abstract]
Net unrealized gains (losses) on cash flow hedge derivatives, after-tax, Beginning balance			151
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)
Other Comprehensive Income Other Adjustments [Abstract]
Other, after tax, Beginning balance			(130)
Net unrealized gains (losses) on non-OTTI securities [Member] | Accounting Standards Update 2018-02 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption					59
Net unrealized gains (losses) on cash flow hedge derivatives [Member] | Accounting Standards Update 2018-02 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption					33
Pension and other postretirement benefit plan adjustments [Member] | Accounting Standards Update 2018-02 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption					(96)
Other [Member] | Accounting Standards Update 2018-02 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption					10
Total [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption					6
Other Comprehensive Income (Loss) Total [Abstract]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning Balance			(142)	(265)
Other comprehensive income (loss), after tax and net of reclassifications into Net income			(1,118)	243
Accumulated Other Comprehensive Income (Loss), Net of Tax, Ending Balance	$ (1,260)	$ (22)	(1,260)	$ (22)
Total [Member] | As Previously Reported [Member]
Other Comprehensive Income (Loss) Total [Abstract]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning Balance			$ (148)
Total [Member] | Accounting Standards Update 2018-02 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption					$ 6