Commitments and Contingencies - Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Commitment and Contingencies [Line Items]
Estimate of possible loss	$ 68
Loss accrual	21
Indirect tax contingency	18
Senior Notes [Member]
Commitment and Contingencies [Line Items]
Debt instrument, face amount	40,800	$ 37,300
Senior Notes Issued By Subsidiaries in Canada and Mexico [Member] | Senior Notes [Member]
Commitment and Contingencies [Line Items]
Debt instrument, face amount	1,200
Parent Company [Member] | Euro Medium Term Notes [Member] | Senior Notes [Member]
Commitment and Contingencies [Line Items]
Debt instrument, face amount	$ 1,200	$ 2,000