Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Allowance for doubtful accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 136	$ 157	$ 185
Charged to Costs and Expenses	16	54	73
Deductions	(20)	(75)	(101)
Balance at End of Period	132	136	157
Deferred tax valuation allowance
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	348	178	150
Charged to Costs and Expenses	(150)	75	(64)
Deductions	(6)	95	92
Balance at End of Period	$ 192	$ 348	$ 178