Accumulated Other Comprehensive Income (Loss) (After-tax Changes by Component) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at beginning of period			$ (23)	$ 77
Amounts arising during the period			21	18
Reclassifications from accumulated other comprehensive income			(4)	(17)
Total other comprehensive income (loss)	$ (23)	$ (7)	17	1
Balance at end of period	(6)	78	(6)	78
Available- for-sale securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at beginning of period			202	173
Amounts arising during the period			(21)	18
Reclassifications from accumulated other comprehensive income			(1)	(5)
Total other comprehensive income (loss)			(22)	13
Balance at end of period	180	186	180	186
Qualifying derivatives
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at beginning of period			63	88
Amounts arising during the period			0	0
Reclassifications from accumulated other comprehensive income			(14)	(18)
Total other comprehensive income (loss)			(14)	(18)
Balance at end of period	49	70	49	70
Prior service costs
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at beginning of period			7	(4)
Amounts arising during the period			(4)	0
Reclassifications from accumulated other comprehensive income			(1)	2
Total other comprehensive income (loss)			(5)	2
Balance at end of period	2	(2)	2	(2)
Actuarial gain (loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at beginning of period			(295)	(180)
Amounts arising during the period			46	0
Reclassifications from accumulated other comprehensive income			12	4
Total other comprehensive income (loss)			58	4
Balance at end of period	$ (237)	$ (176)	$ (237)	$ (176)