Significant Financing Transactions (Schedule of Equity Units) (Parenthetical) (Detail) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended	9 Months Ended
	Jun. 14, 2019	Sep. 30, 2020	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Capital Unit [Line Items]
Issuance costs	$ 28
Corporate units stock purchase contract liability payments			$ 62	$ 17
Stock Purchase Contract Liability		$ 150	150		$ 212
Preferred Stock
Capital Unit [Line Items]
Issuance costs	14
Recorded dividend		$ 7	$ 21
Recorded dividends per share		$ 4.375	$ 13.125
Common Stock
Capital Unit [Line Items]
Issuance costs	$ 14