Accumulated Other Comprehensive Income - Changes in Accumulated Balances of Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss), Tax
Beginning balance, Estimated tax (expense) benefit	$ 25	$ 24
Other comprehensive income (loss) before reclassifications, Estimated tax (expense) benefit	14	(16)
Less: Amount of gain (loss) reclassified from accumulated other comprehensive income, Estimated tax (expense) benefit	(3)	(17)
Net current period other comprehensive income (loss), Estimated tax (expense) benefit	17	1
Ending balance, Estimated tax (expense) benefit	42	25	$ 24
Accumulated Other Comprehensive Income (Loss), Net of Tax
Stockholders' equity, beginning of period	2,870	6,281
Other comprehensive income (loss) before reclassifications, net of tax	244	(50)
Less: Amount of gain (loss) reclassified from accumulated other comprehensive income, net of tax	12	64
Other comprehensive income (loss), net of tax	232	(114)	(219)
Stockholders' equity, end of period	3,561	2,870	6,281
Unrealized Gains (Losses) on Derivative Instruments
Accumulated Other Comprehensive Income (Loss), Before Tax
Beginning balance, before tax	(9)	68
Other comprehensive income (loss) before reclassifications	(61)	4
Less: Amount of gain (loss) reclassified from AOCI	15	81
Net current period other comprehensive income (loss)	(76)	(77)
Ending balance, before tax	(85)	(9)	68
Unrealized Gains (Losses) on Investments
Accumulated Other Comprehensive Income (Loss), Before Tax
Beginning balance, before tax	5	(56)
Other comprehensive income (loss) before reclassifications	0	61
Less: Amount of gain (loss) reclassified from AOCI	0	0
Net current period other comprehensive income (loss)	0	61
Ending balance, before tax	5	5	(56)
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss), Before Tax
Beginning balance, before tax	363	462
Other comprehensive income (loss) before reclassifications	291	(99)
Less: Amount of gain (loss) reclassified from AOCI	0	0
Net current period other comprehensive income (loss)	291	(99)
Ending balance, before tax	654	363	462
AOCI
Accumulated Other Comprehensive Income (Loss), Net of Tax
Stockholders' equity, beginning of period	384	498
Stockholders' equity, end of period	$ 616	$ 384	$ 498