Preferred Stock (Schedule of Equity Units) (Parenthetical) (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Capital Unit [Line Items]
Issuance costs		$ 28
Corporate units stock purchase contract liability payments	$ 83	38
Stock Purchase Contract Liability	129	212
Preferred Stock
Capital Unit [Line Items]
Issuance costs		14
Recorded dividend	$ 28	$ 15
Dividends per share	$ 17.50	$ 9.479
Common Stock
Capital Unit [Line Items]
Issuance costs		$ 14