Indebtedness - Summary of Unsecured Senior Notes (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Unsecured senior notes, net	$ 2,074,000,000	$ 2,366,000,000
Unsecured Senior Notes
Debt Instrument [Line Items]
Unsecured senior notes principal amount	2,100,000,000	2,398,000,000
Unamortized debt issuance costs and discount, net of premium	(26,000,000)	(32,000,000)
Unsecured senior notes, net	2,074,000,000	2,366,000,000
Unsecured Senior Notes \| $850 Face Value, 5.500% interest payable semi-annually, due August 2028
Debt Instrument [Line Items]
Unsecured senior notes principal amount	850,000,000	0
Face amount	$ 850,000,000
Interest rate	5.50%
Unsecured Senior Notes \| $650 Face Value, 5.125% Interest Rate Payable Semi Annually, Due December 2030
Debt Instrument [Line Items]
Unsecured senior notes principal amount	$ 650,000,000	0
Face amount	$ 650,000,000
Interest rate	5.125%
Unsecured Senior Notes \| $600 face value, 6.000% interest rate payable semi-annually, due January 2027
Debt Instrument [Line Items]
Unsecured senior notes principal amount	$ 600,000,000	0
Face amount	$ 600,000,000
Interest rate	6.00%
Unsecured Senior Notes \| $950 face value, 8.125% interest rate payable semi-annually, due July 2023
Debt Instrument [Line Items]
Unsecured senior notes principal amount	$ 0	950,000,000
Face amount	$ 950,000,000
Interest rate	8.125%
Unsecured Senior Notes \| $750 face value, 9.125% interest rate payable semi-annually, due July 2026
Debt Instrument [Line Items]
Unsecured senior notes principal amount	$ 0	750,000,000
Face amount	$ 750,000,000
Interest rate	9.125%
Unsecured Senior Notes \| $600 face value, 6.500% interest rate payable semi-annually, due July 2021
Debt Instrument [Line Items]
Unsecured senior notes principal amount	$ 0	492,000,000
Face amount	$ 600,000,000
Interest rate	6.50%
Unsecured Senior Notes \| $300 face value, 6.500% interest rate payable semi-annually, due June 2022
Debt Instrument [Line Items]
Unsecured senior notes principal amount	$ 0	$ 206,000,000
Face amount	$ 300,000,000
Interest rate	6.50%

Unsecured Debt, Gross

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