- Change in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance, beginning			$ 17,386	$ 16,593
Other comprehensive income (loss) before reclassifications	$ 26	$ (17)	110	395
Amounts reclassified from AOCI	0	(24)	(17)	(76)
Balance, ending	18,579	17,512	18,579	17,512
Net Unrealized Gains (Losses) on Cash Flow Hedges
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance, beginning	(85)	228	(77)	38
Other comprehensive income (loss) before reclassifications	4	(35)	26	208
Amounts reclassified from AOCI	(7)	(24)	(37)	(77)
Balance, ending	(88)	169	(88)	169
Net Unrealized Gains (Losses) on Securities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance, beginning	(149)	(6)	(208)	(152)
Other comprehensive income (loss) before reclassifications	18	19	77	183
Amounts reclassified from AOCI	(1)	(15)	(1)	(33)
Balance, ending	(132)	(2)	(132)	(2)
Foreign Currency Translation Adjustment
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance, beginning	(19)	(19)	(22)	(24)
Other comprehensive income (loss) before reclassifications	4	(1)	7	4
Amounts reclassified from AOCI	0	0	0	0
Balance, ending	(15)	(20)	(15)	(20)
Pension and Other Benefits Adjustment
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance, beginning	(576)	(593)	(589)	(612)
Other comprehensive income (loss) before reclassifications	0	0	0	0
Amounts reclassified from AOCI	7	16	20	35
Balance, ending	(569)	(577)	(569)	(577)
Accumulated Other
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance, beginning	0	0	0	0
Other comprehensive income (loss) before reclassifications	0	0	0	0
Amounts reclassified from AOCI	1	(1)	1	(1)
Balance, ending	1	(1)	1	(1)
Accumulated Other Comprehensive Loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance, beginning	(829)	(390)	(896)	(750)
Balance, ending	$ (803)	$ (431)	$ (803)	$ (431)