Accumulated Other Comprehensive Income Reclassifications out of AOCI (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	$ 302	$ 169	$ 302	$ 169	$ 183	$ 298	$ 206	$ (77)
Other Comprehensive Income (Loss), Reclassification Adjustment for Sale of Securities Included in Net Income, before Tax	(7)	9	(21)	11
Other Comprehensive Income (Loss), Reclassification Adjustment for Sale of Securities Included in Net Income, Tax	3	(3)	8	(4)
Other Comprehensive Income (Loss), Reclassification Adjustment for Sale of Securities Included in Net Income, Net of Tax	(4)	6	(13)	7
Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, before Tax	(70)	(99)	(187)	(302)
Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, Tax	26	36	69	111
Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, Net of Tax	(44)	(63)	(118)	(191)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, before Tax	4	2	(108)	54
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Tax	(1)	(1)	44	(20)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	3	1	(64)	34
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(45)	(56)	(195)	(150)
Other Assets And Liabilities, Net [Member]
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, before Tax	0	0	(120)	46
Amortization of Actuarial Loss [Member]
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, before Tax	5	4	16	12
Amortization of Prior Service Credit [Member]
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, before Tax	$ (1)	$ (2)	$ (4)	$ (4)