Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Accumulated Other Comprehensive Income (Loss), Tax [Roll Forward]
Accumulated other comprehensive income (loss) tax provision (benefit), beginning balance	$ (316)	$ (225)
Other comprehensive income before reclassifications, tax	39	(57)
Amounts reclassified from accumulated other comprehensive income, tax	0	0
Net current period other comprehensive income, tax	39	(57)
Accumulated other comprehensive income (loss) tax provision (benefit), ending balance	(277)	(282)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss), net of tax, beginning balance	1,156	856
Other comprehensive income before reclassifications	(86)	(135)
Amounts reclassified from other comprehensive income	(14)	(3)
Other comprehensive income (loss), net tax	(72)	(132)
Accumulated other comprehensive income (loss), net of tax, ending balance	1,084	724
Unrealized Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss), Before Tax [Roll Forward]
Accumulated other comprehensive income (loss), before tax, beginning balance	(106)	(55)
Other comprehensive income, before reclassifications, before tax	(6)	82
Amounts reclassified from accumulated other comprehensive income, before tax	(21)	(4)
Net current period other comprehensive income , before tax	15	86
Accumulated other comprehensive income (loss), before tax, ending balance	(91)	31
Unrealized Gains on Investments
Accumulated Other Comprehensive Income (Loss), Before Tax [Roll Forward]
Accumulated other comprehensive income (loss), before tax, beginning balance	921	687
Other comprehensive income, before reclassifications, before tax	(90)	141
Amounts reclassified from accumulated other comprehensive income, before tax	7	1
Net current period other comprehensive income , before tax	(97)	140
Accumulated other comprehensive income (loss), before tax, ending balance	824	827
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss), Before Tax [Roll Forward]
Accumulated other comprehensive income (loss), before tax, beginning balance	657	449
Other comprehensive income, before reclassifications, before tax	(29)	(301)
Amounts reclassified from accumulated other comprehensive income, before tax	0	0
Net current period other comprehensive income , before tax	(29)	(301)
Accumulated other comprehensive income (loss), before tax, ending balance	$ 628	$ 148