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Summary of Accounting Policies - Impact of Adopting New Accounting Standards (Details) - USD ($) $ in Millions	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets
Accounts receivable	$ 7,071		$ 6,873
Liabilities
Income taxes payable	1,971		708
Debt	5,308		3,057
Deferred Income Taxes	1,702		2,219
Equity
Retained earnings	42,579		41,350
Accumulated other comprehensive loss	(5,545)		$ (4,910)
ASU 2016-01 (Financial Instruments)
Equity
Retained earnings		$ 8
Accumulated other comprehensive loss		(8)
ASU 2016-16 (Intra-Entity Transfers Other than Inventory)
Liabilities
Deferred Income Taxes	(54)	(54)
Equity
Retained earnings		54
ASU 2017-12 (Derivatives and Hedging)
Liabilities
Income taxes payable		(3)
Debt		14
Equity
Retained earnings		(11)
ASU 2018-02 (Reclassification of Certain Tax Effects)
Equity
Retained earnings		266
Accumulated other comprehensive loss		(266)
Adjustments for New Accounting Pronouncement
Assets
Accounts receivable		5
Liabilities
Income taxes payable		(3)
Debt		14
Deferred Income Taxes		(54)
Equity
Retained earnings		322
Accumulated other comprehensive loss		(274)
Effects of Adopting ASC 606 \| ASU 2014-09 (Revenue)
Assets
Accounts receivable	(13)	5
Liabilities
Income taxes payable	(1)
Equity
Retained earnings	$ (2)	$ 5