Accumulated Other Comprehensive Income (Details 2) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Change in accumulated other comprehensive loss balances:
Beginning Balance	$ 17,233
Ending Balance	17,484
Net Unrealized Gains (Losses) on Cash Flow Hedges
Change in accumulated other comprehensive loss balances:
Beginning Balance	(77)	$ 38
Other comprehensive income (loss) before reclassifications	(12)	158
Amounts reclassified from AOCI	(18)	(26)
Ending Balance	(107)	170
Net Unrealized Gains (Losses) on Securities
Change in accumulated other comprehensive loss balances:
Beginning Balance	(208)	(152)
Other comprehensive income (loss) before reclassifications	36	98
Amounts reclassified from AOCI	(1)	(8)
Ending Balance	(173)	(62)
Foreign Currency Translation Adjustment
Change in accumulated other comprehensive loss balances:
Beginning Balance	(22)	(24)
Other comprehensive income (loss) before reclassifications	1	4
Amounts reclassified from AOCI	0	0
Ending Balance	(21)	(20)
Pension and Other Benefits Adjustment
Change in accumulated other comprehensive loss balances:
Beginning Balance	(589)	(612)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from AOCI	7	10
Ending Balance	(582)	(602)
Accumulated Other
Change in accumulated other comprehensive loss balances:
Beginning Balance	0	0
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from AOCI	0	(2)
Ending Balance	0	(2)
Accumulated Other Comprehensive Loss
Change in accumulated other comprehensive loss balances:
Beginning Balance	(896)	(750)
Other comprehensive income (loss) before reclassifications	25	260
Amounts reclassified from AOCI	(12)	(26)
Ending Balance	$ (883)	$ (516)