SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS - Schedule of Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	$ 2,384	$ 2,546
Charged to Other Accounts	5,287	5,887
Deductions	(5,637)	(6,049)
Balance at End of Year	2,050	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	47	97	80
Charged to Costs and Expenses	10	4	33
Charged to Other Accounts	(1)	(4)	4
Deductions	(8)	(50)	(20)
Balance at End of Year	48	47	97
Deferred tax asset valuation allowance
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	2,913	2,001	1,857
Charged to Costs and Expenses	13	870	221
Charged to Other Accounts	(95)	42	(77)
Deductions	0	0	0
Balance at End of Year	$ 2,831	$ 2,913	$ 2,001