Series A Convertible Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended			9 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Oct. 13, 2020	Oct. 06, 2020	Dec. 31, 2019	Sep. 18, 2019	Mar. 17, 2017	Dec. 04, 2015
Class of Stock [Line Items]
Temporary Equity, Shares Issued		400,000		400,000				400,000
Secondary offering by the preferred shareholders										342,000
Redeemed Shares of Preferred Stock										90,000
Repurchase price per share of common stock upon conversion										$ 48.47
Deemed Dividend on Preferred Stock Redemption		$ 0	$ 67	$ 0	$ 67
Series A Convertible Preferred Stock
Class of Stock [Line Items]
Temporary Equity, Shares Issued											820,000
Aggregate purchase price of preferred shares											$ 820
Preferred stock, par value (in dollars per share)											$ 1,000
Direct issuance expenses											$ 26
Dividend rate											5.50%
Conversion price per share at option of holder (in dollars per share)											$ 30.00
Conversion rate per preferred share (in shares)				33.333
Redeemed Shares of Preferred Stock									512,221
Blackstone Shares Converted into Common Shares									237,673
Cash Paid for the Redemption of Preferred Stock									$ 302
Preferred Shares Converted into Common Stock in Redemption			9,160,000
Dividends, preferred stock, paid-in-kind		6	$ 13	$ 13	$ 37
Dividends, Preferred Stock				19
Dividends, Preferred Stock, Cash		6
Accrued Dividends		$ 1		$ 1				$ 1
Financial instruments subject to redemption, settlement terms, maximum number of shares (in shares)		13,700,000		13,700,000				13,300,000
Series A Convertible Preferred Stock | Subsequent Event [Member]
Class of Stock [Line Items]
Cash Paid for the Redemption of Preferred Stock						$ 72	$ 72
Dividends, Preferred Stock, Cash	$ 7
Preferred Shares Redeemed						65,365	67,000
Reduction to financial instruments subject to redemption settlement terms, maximum number of shares	4,400,000
Common Stock [Member]
Class of Stock [Line Items]
Preferred Shares Converted into Common Stock in Redemption			9,000,000