- Change in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance, beginning			$ 18,355	$ 17,386
Other comprehensive income (loss) before reclassifications			(364)	110
Other Comprehensive Income (Loss), Net of Tax	$ (28)	$ 26	(308)	93
Amounts reclassified from AOCI			56	(17)
Balance, ending	18,822	18,579	18,822	18,579
Net Unrealized Gains (Losses) on Cash Flow Hedges
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance, beginning	(240)	(85)	(174)	(77)
Other comprehensive income (loss) before reclassifications	0	4	(72)	26
Amounts reclassified from AOCI	8	(7)	14	(37)
Transfer to additional paid-in capital			0
Balance, ending	(232)	(88)	(232)	(88)
Net Unrealized Gains (Losses) on Securities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance, beginning	(464)	(149)	(233)	(208)
Other comprehensive income (loss) before reclassifications	(51)	18	(289)	77
Amounts reclassified from AOCI	5	(1)	12	(1)
Transfer to additional paid-in capital			0
Balance, ending	(510)	(132)	(510)	(132)
Foreign Currency Translation Adjustment
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance, beginning	0	(19)	(19)	(22)
Other comprehensive income (loss) before reclassifications	0	4		7
Other Comprehensive Income (Loss), Net of Tax			(2)
Amounts reclassified from AOCI	0	0	0	0
Transfer to additional paid-in capital			21
Balance, ending	0	(15)	0	(15)
Pension and Other Benefits Adjustment
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance, beginning	(580)	(576)	(600)	(589)
Other comprehensive income (loss) before reclassifications	0	0	0	0
Amounts reclassified from AOCI	10	7	30	20
Transfer to additional paid-in capital			0
Balance, ending	(570)	(569)	(570)	(569)
Accumulated Other
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance, beginning	(1)	0	0	0
Other comprehensive income (loss) before reclassifications	0	0	(1)	0
Amounts reclassified from AOCI	0	1	0	1
Transfer to additional paid-in capital			0
Balance, ending	(1)	1	(1)	1
Accumulated Other Comprehensive Income (Loss)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance, beginning	(1,285)	(829)	(1,026)	(896)
Other comprehensive income (loss) before reclassifications	(51)	26
Other Comprehensive Income (Loss), Net of Tax			(308)	93
Amounts reclassified from AOCI	23	0
Transfer to additional paid-in capital			21
Balance, ending	$ (1,313)	$ (803)	$ (1,313)	$ (803)