SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS - Schedule of Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	$ 2,546
Charged to Other Accounts	5,887
Deductions	(6,049)
Balance at End of Year	2,384	$ 2,546
Allowance for doubtful accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	97	80	$ 67
Charged to Costs and Expenses	4	33	57
Charged to Other Accounts	(4)	4	(22)
Deductions	(50)	(20)	(22)
Balance at End of Year	47	97	80
Deferred tax asset valuation allowance
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	2,001	1,857	1,367
Charged to Costs and Expenses	870	221	627
Charged to Other Accounts	42	(77)	(137)
Deductions	0	0	0
Balance at End of Year	$ 2,913	$ 2,001	$ 1,857