Debt - Holding Company Debt (Details) - Holding Company - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Jan. 31, 2021	Jan. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	May 31, 2019	Dec. 31, 2017	Jan. 31, 2017
Debt Instrument [Line Items]
(Gain) loss on extinguishment of debt	$ (4)	$ 2
6.000% senior unsecured notes due 2020
Debt Instrument [Line Items]
Interest rate on debt instrument						6.00%	6.00%
5.875% senior unsecured notes due 2022
Debt Instrument [Line Items]
Interest rate on debt instrument	5.875%
Repayment of senior notes	$ 1,350
6.250% senior unsecured notes due 2022
Debt Instrument [Line Items]
Debt face amount								$ 510	$ 695
Interest rate on debt instrument	6.25%							6.25%	6.25%
6.250% senior unsecured notes due 2022 | Subsequent event
Debt Instrument [Line Items]
Debt face amount			$ 750
Interest rate on debt instrument			6.25%
6.750% senior unsecured notes due 2024
Debt Instrument [Line Items]
Debt face amount									$ 500
Interest rate on debt instrument	6.75%								6.75%
4.750% senior unsecured notes due 2024
Debt Instrument [Line Items]
Debt face amount				$ 600	$ 500
Interest rate on debt instrument	4.75%			4.75%	4.75%
6.375% senior unsecured notes due 2025
Debt Instrument [Line Items]
Debt face amount								$ 750
Interest rate on debt instrument	6.375%							6.375%
6.250% senior unsecured notes due 2026
Debt Instrument [Line Items]
Debt face amount						$ 1,250	$ 1,250
Interest rate on debt instrument	6.25%					6.25%	6.25%
5.250% senior unsecured notes due 2027
Debt Instrument [Line Items]
Debt face amount	$ 250	$ 750
Interest rate on debt instrument	5.25%	5.25%
4.375% senior unsecured notes due 2029 | Subsequent event
Debt Instrument [Line Items]
Debt face amount			$ 750
Interest rate on debt instrument			4.375%