Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Employee Termination Benefits
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at January 1	$ 19	$ 62	$ 111
Additions (reductions) charged to expense	6	5	20
Payments/ reductions	(18)	(48)	(69)
Balance at December 31	7	19	62
Allowance for Doubtful Accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at January 1	980	606	487
Additions (reductions) charged to expense	(128)	379	128
Payments/ reductions	(3)	(5)	(9)
Balance at December 31	849	980	606
Deferred Income Tax Valuation Allowance
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at January 1	15,973	16,574	16,069
Additions (reductions) charged to expense	1,336	2,000	2,681
Payments/ reductions	(1,344)	(2,601)	(2,176)
Balance at December 31	$ 15,965	$ 15,973	$ 16,574