Debt - Interest Expense (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Debt Instrument [Line Items]
Total interest cost	$ 417	$ 471
Capitalized interest	(61)	(59)
Total interest expense, net of capitalized interest	356	412
Convertible Debt [Member]
Debt Instrument [Line Items]
Interest per contractual rate	12	63
Amortization of debt discount	5	14
Amortization of debt issuance costs	0	3
Total interest cost	17	80
Debt and Finance Leases Excluding Convertible Debt [Member]
Debt Instrument [Line Items]
Total interest cost	$ 400	$ 391