Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss), Tax
Beginning balance, Estimated tax (expense) benefit	$ 24	$ 41
Other comprehensive income (loss) before reclassifications, Estimated tax (expense) benefit	(16)	(15)
Less: Amount of gain (loss) reclassified from accumulated other comprehensive income, Estimated tax (expense) benefit	(17)	2
Net current period other comprehensive income (loss), Estimated tax (expense) benefit	1	(17)
Ending balance, Estimated tax (expense) benefit	25	24	$ 41
Accumulated Other Comprehensive Income (Loss), Net of Tax
Stockholders' equity, beginning of period	6,281	8,049
Other comprehensive income (loss) before reclassifications, net of tax	(50)	(226)
Less: Amount of gain (loss) reclassified from accumulated other comprehensive income, net of tax	64	(7)
Other comprehensive income (loss), net of tax	(114)	(219)	841
Stockholders' equity, end of period	2,870	6,281	8,049
Unrealized Gains (Losses) on Derivative Instruments
Accumulated Other Comprehensive Income (Loss), Before Tax
Beginning balance, before tax	68	(57)
Other comprehensive income (loss) before reclassifications	4	117
Less: Amount of gain (loss) reclassified from AOCI	81	(8)
Net current period other comprehensive income (loss)	(77)	125
Ending balance, before tax	(9)	68	(57)
Unrealized Gains (Losses) on Investments
Accumulated Other Comprehensive Income (Loss), Before Tax
Beginning balance, before tax	(56)	(15)
Other comprehensive income (loss) before reclassifications	61	(42)
Less: Amount of gain (loss) reclassified from AOCI	0	(1)
Net current period other comprehensive income (loss)	61	(41)
Ending balance, before tax	5	(56)	(15)
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss), Before Tax
Beginning balance, before tax	462	748
Other comprehensive income (loss) before reclassifications	(99)	(286)
Less: Amount of gain (loss) reclassified from AOCI	0	0
Net current period other comprehensive income (loss)	(99)	(286)
Ending balance, before tax	363	462	748
AOCI
Accumulated Other Comprehensive Income (Loss), Net of Tax
Stockholders' equity, beginning of period	498	717
Stockholders' equity, end of period	$ 384	$ 498	$ 717