Recent Accounting Pronouncements - Recently Issued Accounting Pronouncements (Details) - Accounting Standards Update 2017-07 - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Gross profit
Recently Issued Accounting Pronouncements [Line Items]
Reported after adoption of new accounting pronouncement	$ 656	$ 700
Financial statement line item as reported	665	705
Operating profit
Recently Issued Accounting Pronouncements [Line Items]
Reported after adoption of new accounting pronouncement	353	396
Financial statement line item as reported	367	394
Other net periodic postretirement benefit (costs)
Recently Issued Accounting Pronouncements [Line Items]
Reported after adoption of new accounting pronouncement	14	(2)
Financial statement line item as reported	0	0
Net income
Recently Issued Accounting Pronouncements [Line Items]
Reported after adoption of new accounting pronouncement	88	510
Financial statement line item as reported	$ 88	$ 510