Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss) Tax Provision (Benefit)	$ (316)	$ (225)
Other comprehensive income before reclassifications, tax	(44)	(91)
Amount of gain (loss) reclassified from accumulated other comprehensive income, tax	0	0
Net current period other comprehensive income, tax	44	91
Accumulated Other Comprehensive Income (Loss), Net of Tax	1,156	856
Other comprehensive income before reclassifications, net of tax	31	295
Amount of gain (loss( reclassified form accumulated other comprehensive income, net of tax	16	(5)
Net current period other comprehensive income, net of tax	15	300
Accumulated Other Comprehensive Income (Loss) Tax (Expense) Benefit	(360)	(316)
Accumulated Other Comprehensive Income (Loss), Net of Tax	1,171	1,156
Unrealized Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), before Tax	(106)	(55)
Other comprehensive income before reclassifications	238	(65)
Amount of gain (loss) reclassified from accumulated other comprehensive income	(36)	(14)
Net current period comprehensive income	274	(51)
Accumulated Other Comprehensive Income (Loss), before Tax	168	(106)
Unrealized Gains on Investments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), before Tax	921	687
Other comprehensive income before reclassifications	160	243
Amount of gain (loss) reclassified from accumulated other comprehensive income	52	9
Net current period comprehensive income	108	234
Accumulated Other Comprehensive Income (Loss), before Tax	1,029	921
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), before Tax	657	449
Other comprehensive income before reclassifications	(323)	208
Amount of gain (loss) reclassified from accumulated other comprehensive income	0	0
Net current period comprehensive income	(323)	208
Accumulated Other Comprehensive Income (Loss), before Tax	$ 334	$ 657