Subsequent Event (Details) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended		3 Months Ended	12 Months Ended
	Jan. 15, 2021	Feb. 16, 2021	Jan. 31, 2021	Jan. 28, 2021	Dec. 31, 2020	Jan. 29, 2021	Oct. 22, 2020
Prior ATM
Subsequent Event [Line Items]
Common stock, shares authorized, value							$ 1,000
Issuance of shares of common stock, net of offering costs (in shares)					68,561,487
Common shares, stock price (in dollars per share)					$ 12.87		$ 12.87
Proceeds from issuance of common stock					$ 869
Subsequent Event | Prior ATM
Subsequent Event [Line Items]
Issuance of shares of common stock, net of offering costs (in shares)				68,600,000
Proceeds from issuance of common stock				$ 869
Common stock, remaining authorized amount available for issuance				$ 118
Subsequent Event | New ATM
Subsequent Event [Line Items]
Common stock, shares authorized, value						$ 1,100
Issuance of shares of common stock, net of offering costs (in shares)		18,200,000
Common shares, stock price (in dollars per share)						$ 17.59
Proceeds from issuance of common stock		$ 320
PSP2, CAREs Act | Subsequent Event
Subsequent Event [Line Items]
Debt instrument, agreed amount under PSP2	$ 896
Number of warrants authorized (in shares)	5,700,000		2,800,000
Aggregate principal issued	$ 433		$ 433
Increase in debt instrument face amount for each installment disbursed (in percentage)	30.00%
Exercise price of warrants (in dollars per share)	$ 15.66
Number of warrants issued	2,800,000
Class of warrant, additional warrants, percentage of borrowing (in percentage)	0.10
PSP2, CAREs Act | Subsequent Event | Interest Rate First Five Years
Subsequent Event [Line Items]
Fixed interest rate per annum	1.00%
PSP2, CAREs Act | Subsequent Event | Interest Rate Years Six Through Ten | Secured Overnight Financing Rate or Other
Subsequent Event [Line Items]
Basis spread on variable rate	2.00%
Floor interest rate	0.00%
US Department Of The Treasury, CARES Act, Payroll Support Program Two | Subsequent Event
Subsequent Event [Line Items]
Total financial assistance through PSP2 (at least)	$ 3,000		3,000
Proceeds from government assistance, payroll support program, CARES Act	$ 1,500		$ 1,500