Fair Value Measurements - Schedule of Assets Measured at Fair Value on a Recurring Basis (Details) - Fair Value Recurring Basis - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Assets:
Restricted cash and investments	$ 47	$ 48
Marketable securities	31	33
Total assets at fair value	78	121
Liabilities:
Total liabilities at fair value	552	416
Level 1
Assets:
Restricted cash and investments	1	1
Marketable securities	20	23
Total assets at fair value	21	24
Liabilities:
Total liabilities at fair value	0	0
Level 2
Assets:
Restricted cash and investments	1	3
Marketable securities	11	10
Total assets at fair value	12	53
Liabilities:
Total liabilities at fair value	552	416
Level 3
Assets:
Restricted cash and investments	45	44
Marketable securities	0	0
Total assets at fair value	45	44
Liabilities:
Total liabilities at fair value	0	0
Foreign Exchange Contract
Assets:
Derivative instruments - FX forward		40
Foreign Exchange Contract | Level 1
Assets:
Derivative instruments - FX forward		0
Foreign Exchange Contract | Level 2
Assets:
Derivative instruments - FX forward		40
Foreign Exchange Contract | Level 3
Assets:
Derivative instruments - FX forward		0
5% Convertible Notes
Liabilities:
Derivative instruments	477	326
5% Convertible Notes | Level 1
Liabilities:
Derivative instruments	0	0
5% Convertible Notes | Level 2
Liabilities:
Derivative instruments	477	326
5% Convertible Notes | Level 3
Liabilities:
Derivative instruments	0	0
Interest Rate Swap
Liabilities:
Derivative instruments	75	90
Interest Rate Swap | Level 1
Liabilities:
Derivative instruments	0	0
Interest Rate Swap | Level 2
Liabilities:
Derivative instruments	75	90
Interest Rate Swap | Level 3
Liabilities:
Derivative instruments	$ 0	$ 0