Quarterly Consolidated Financial Information - Schedule of Quarterly Consolidated Financial Information (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018
Quarterly Financial Information Disclosure [Abstract]
Losses (gains) on sales of facilities	$ 305		$ 14	$ 1	$ 6	$ 5	$ 8
Losses on retirement of debt		$ 162				$ 7