Debt - Debentures (Details) - Unsecured debt	3 Months Ended
	Mar. 31, 2021
7.950% Debentures due 2025
Debt Instrument [Line Items]
Maturity date	Dec. 15, 2025
Semi-annual interest payment dates	June 15 and December 15
8.375% Debentures due 2027
Debt Instrument [Line Items]
Maturity date	Apr. 15, 2027
Semi-annual interest payment dates	April 15 and October 15