Schedule II, Valuation and Qualifying Accounts (Details) - Allowance for Bad Debts - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Jan. 1		$ 6	$ 6	$ 5
Charged to costs and expenses		7	7	4
Charged to other accounts	[1]	1	2	1
Deductions from reserves	[2]	(6)	(9)	(4)
Balance at Dec. 31		$ 8	$ 6	$ 6

[1] Recovery of amounts previously written-off.

[2] Deductions related primarily to bad debt write-offs.