Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Accumulated Other Comprehensive Income (Loss), Before Tax [Roll Forward]
Accumulated other comprehensive income (loss), before tax, beginning balance			$ 1,156
Accumulated other comprehensive income (loss), before tax, ending balance	1,231		1,231
Accumulated Other Comprehensive Income (Loss), Tax [Roll Forward]
Accumulated other comprehensive income (loss) tax provision (benefit), beginning balance	(277)	(282)	(316)	(225)
Other comprehensive income before reclassifications, tax	(11)	(35)	28	(92)
Amounts reclassified from accumulated other comprehensive income, tax	0	0	0	0
Net current period other comprehensive income, tax	(11)	(35)	28	(92)
Accumulated other comprehensive income (loss) tax provision (benefit), ending balance	(288)	(317)	(288)	(317)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss), net of tax, beginning balance	1,084	724	1,156	856
Other comprehensive income before reclassifications	127	105	41	(30)
Amounts reclassified from other comprehensive income	(20)	3	(34)	0
Other comprehensive income (loss), net tax	147	102	75	(30)
Accumulated other comprehensive income (loss), net of tax, ending balance	1,231	826	1,231	826
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	(91)	31	(106)	(55)
Other comprehensive income, before reclassifications, before tax	(5)	25	(11)	107
Amounts reclassified from accumulated other comprehensive income, before tax	(27)	0	(48)	(4)
Net current period other comprehensive income , before tax	22	25	37	111
Accumulated other comprehensive income (loss), before tax, ending balance	(69)	56	(69)	56
Unrealized Gains on Investments
Accumulated Other Comprehensive Income (Loss), Before Tax [Roll Forward]
Accumulated other comprehensive income (loss), before tax, beginning balance	824	827	921	687
Other comprehensive income, before reclassifications, before tax	23	79	(67)	220
Amounts reclassified from accumulated other comprehensive income, before tax	7	3	14	4
Net current period other comprehensive income , before tax	16	76	(81)	216
Accumulated other comprehensive income (loss), before tax, ending balance	840	903	840	903
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss), Before Tax [Roll Forward]
Accumulated other comprehensive income (loss), before tax, beginning balance	628	148	657	449
Other comprehensive income, before reclassifications, before tax	120	36	91	(265)
Amounts reclassified from accumulated other comprehensive income, before tax	0	0	0	0
Net current period other comprehensive income , before tax	120	36	91	(265)
Accumulated other comprehensive income (loss), before tax, ending balance	$ 748	$ 184	$ 748	$ 184