Schedule II - Valuation and Qualifying Accounts (Details) - Allowance for doubtful accounts - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Valuation Allowances [Roll Forward]
Balance at beginning of year	$ 34	$ 33	$ 28
Net charges to income	17	21	15
Deductions and other	(17)	(20)	(11)
Balance at end of year	$ 34	$ 34	$ 33