Financing Agreements - Junior Subordinated Notes (Details) - Junior Subordinated Notes - USD ($) $ in Millions			12 Months Ended
	Jan. 23, 2018	May 16, 2013	Dec. 31, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Maximum deferral period for one or more consecutive interest payments			5 years
5.65% Fixed-to-Floating Rate Junior Subordinated Notes, due 2053
Debt Instrument [Line Items]
Annual interest rate on loan		5.65%	5.65%	5.65%
Description of variable rate basis		LIBOR
Basis spread		3.58%
Amount of unsecured notes issued		$ 750
4.7% Fixed-to-Floating Rate Junior Subordinated Notes, due 2048
Debt Instrument [Line Items]
Annual interest rate on loan	4.70%		4.70%	4.70%
Description of variable rate basis	LIBOR
Basis spread	2.084%
Amount of unsecured notes issued	$ 350