Total Equity and Other Comprehensive Income (Accumulated Other Comprehensive Income (Loss) Components) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 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	$ 121	$ 52
Other Comprehensive Income (Loss), Non Otti Securities Adjustment, After Tax	(496)	44
Net unrealized gains (losses) on non-OTTI securities, after-tax, Ending Balance	(375)	96
Net Unrealized Gains Losses On Otti Securities [Abstract]
Net unrealized gains (losses) on OTTI securities, after tax, Beginning Balance	215	106
Other Comprehensive Income Loss Otti Securities Adjustment After Tax	10	22
Net unrealized gains (losses) on OTTI securities, after tax, Ending Balance	225	128
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax [Abstract]
Net unrealized gains (losses) on cash flow hedge derivatives, after-tax, Beginning balance	184	333
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	(149)	(49)
Net unrealized gains (losses) on cash flow hedge derivatives, after-tax, Ending balance	35	284
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, before Tax [Abstract]
Pension and other postretirement benefit plan adjustments, after tax, Beginning Balance	(542)	(553)
Pension and other postretirement benefit plan adjustments, net activity, After Tax	48	(39)
Pension and other postretirement benefit plan adjustments, after tax, Ending Balance	(494)	(592)
Other Comprehensive Income Other Adjustments [Abstract]
Other, after tax, Beginning balance	(120)	(203)
Total Other, net activity, After tax	30	8
Other, after tax, Ending balance	(90)	(195)
Accumulated Other Comprehensive Income (Loss), Net of Tax, Adjusted Balance			(142)
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning Balance	(148)	(265)
Other comprehensive income (loss), after tax and net of reclassifications into Net income	(557)	(14)
Accumulated Other Comprehensive Income (Loss), Net of Tax, Ending Balance	(699)	(279)
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 Other Adjustments [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	(557)	(14)
Accumulated Other Comprehensive Income (Loss), Net of Tax, Ending Balance	(699)	$ (279)
Total [Member] | As Previously Reported [Member]
Other Comprehensive Income Other Adjustments [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