Series A Convertible Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Sep. 18, 2019	Mar. 17, 2017	Dec. 04, 2015
Class of Stock [Line Items]
Series A convertible preferred stock, issued (in shares)	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
Series A Convertible Preferred Stock
Class of Stock [Line Items]
Series A convertible preferred stock, issued (in shares)						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, Cash	$ 6
Dividends, preferred stock, paid-in-kind		$ 12
Financial instruments subject to redemption, settlement terms, maximum number of shares (in shares)	13,200,000		13,300,000