Accumulated Other Comprehensive Income - Changes in Accumulated Balances of Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Accumulated Other Comprehensive Income (Loss), Tax
Beginning balance	$ 23	$ 23	$ 25	$ 24
Other comprehensive income (loss) before reclassifications	(2)	(10)	(4)	(15)
Less: Amount of gain (loss) reclassified from AOCI	(4)	(3)	(4)	(7)
Net current period other comprehensive income (loss)	2	(7)	0	(8)
Ending balance	25	16	25	16
Accumulated Other Comprehensive Income (Loss), Net of Tax
Beginning balance			2,870
Other comprehensive income (loss) before reclassifications	49	11	(50)	(7)
Less: Amount of gain (loss) reclassified from AOCI	13	11	13	27
Other comprehensive income (loss), net of tax	36	0	(63)	(34)
Ending balance	2,902	4,106	2,902	4,106
Unrealized Gains (Losses) on Derivative Instruments
Accumulated Other Comprehensive Income (Loss), Before Tax
Beginning balance	38	27	(9)	68
Other comprehensive income (loss) before reclassifications	(30)	25	17	4
Less: Amount of gain (loss) reclassified from AOCI	17	14	17	34
Net current period other comprehensive income (loss)	(47)	11	0	(30)
Ending balance	(9)	38	(9)	38
Unrealized Gains (Losses) on Investments
Accumulated Other Comprehensive Income (Loss), Before Tax
Beginning balance	(26)	(16)	5	(56)
Other comprehensive income (loss) before reclassifications	32	16	1	56
Less: Amount of gain (loss) reclassified from AOCI	0	0	0	0
Net current period other comprehensive income (loss)	32	16	1	56
Ending balance	6	0	6	0
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss), Before Tax
Beginning balance	250	430	363	462
Other comprehensive income (loss) before reclassifications	49	(20)	(64)	(52)
Less: Amount of gain (loss) reclassified from AOCI	0	0	0	0
Net current period other comprehensive income (loss)	49	(20)	(64)	(52)
Ending balance	299	410	299	410
Total
Accumulated Other Comprehensive Income (Loss), Net of Tax
Beginning balance	285	464	384	498
Ending balance	$ 321	$ 464	$ 321	$ 464