Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Accumulated Other Comprehensive Income (Loss), Tax
Accumulated other comprehensive income (loss) tax provision (benefit), beginning balance	$ (360)	$ (316)
Other comprehensive income before reclassifications, tax	7	39
Amount of gain (loss) reclassified from accumulated other comprehensive income, tax	0	0
Net current period other comprehensive income, tax	7	39
Accumulated other comprehensive income (loss) tax provision (benefit), ending balance	(353)	(277)
Accumulated Other Comprehensive Income (Loss), Net of Tax
Accumulated other comprehensive income (loss), net of tax, beginning balance	1,171	1,156
Other comprehensive income before reclassifications	(122)	(86)
Amount of gain (loss) reclassified from accumulated other comprehensive income	69	(14)
Other comprehensive income (loss), net tax	(191)	(72)
Accumulated other comprehensive income (loss), net of tax, ending balance	980	1,084
Unrealized Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss), Before Tax
Accumulated other comprehensive income (loss), before tax, beginning balance	168	(106)
Other comprehensive income, before reclassifications, before tax	159	(6)
Amount of gain (loss) reclassified from accumulated other comprehensive income, before tax	70	(21)
Net current period other comprehensive income , before tax	89	15
Accumulated other comprehensive income (loss), before tax, ending balance	257	(91)
Unrealized Gains on Investments
Accumulated Other Comprehensive Income (Loss), Before Tax
Accumulated other comprehensive income (loss), before tax, beginning balance	1,029	921
Other comprehensive income, before reclassifications, before tax	(23)	(90)
Amount of gain (loss) reclassified from accumulated other comprehensive income, before tax	(1)	7
Net current period other comprehensive income , before tax	(22)	(97)
Accumulated other comprehensive income (loss), before tax, ending balance	1,007	824
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss), Before Tax
Accumulated other comprehensive income (loss), before tax, beginning balance	334	657
Other comprehensive income, before reclassifications, before tax	(265)	(29)
Amount of gain (loss) reclassified from accumulated other comprehensive income, before tax	0	0
Net current period other comprehensive income , before tax	(265)	(29)
Accumulated other comprehensive income (loss), before tax, ending balance	$ 69	$ 628