- Change in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 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			(313)	84
Other Comprehensive Income (Loss), Net of Tax	$ (39)	$ 54	(280)	67
Amounts reclassified from AOCI			33	(17)
Balance, ending	18,547	17,937	18,547	17,937
Net Unrealized Gains (Losses) on Cash Flow Hedges
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance, beginning	(232)	(107)	(174)	(77)
Other comprehensive income (loss) before reclassifications	(14)	34	(72)	22
Amounts reclassified from AOCI	6	(12)	6	(30)
Transfer to additional paid-in capital			0
Balance, ending	(240)	(85)	(240)	(85)
Net Unrealized Gains (Losses) on Securities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance, beginning	(423)	(173)	(233)	(208)
Other comprehensive income (loss) before reclassifications	(45)	26	(238)	59
Amounts reclassified from AOCI	4	(2)	7	0
Transfer to additional paid-in capital			0
Balance, ending	(464)	(149)	(464)	(149)
Foreign Currency Translation Adjustment
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance, beginning	0	(21)	(19)	(22)
Other comprehensive income (loss) before reclassifications	0	2		3
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	(19)	0	(19)
Pension and Other Benefits Adjustment
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance, beginning	(590)	(582)	(600)	(589)
Other comprehensive income (loss) before reclassifications	0	0	0	0
Amounts reclassified from AOCI	10	6	20	13
Transfer to additional paid-in capital			0
Balance, ending	(580)	(576)	(580)	(576)
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	0	0	0
Transfer to additional paid-in capital			0
Balance, ending	(1)	0	(1)	0
Accumulated Other Comprehensive Loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance, beginning	(1,246)	(883)	(1,026)	(896)
Other comprehensive income (loss) before reclassifications	(59)	62
Other Comprehensive Income (Loss), Net of Tax			(280)	67
Amounts reclassified from AOCI	20	(8)
Transfer to additional paid-in capital			21
Balance, ending	$ (1,285)	$ (829)	$ (1,285)	$ (829)