Basis of Presentation - Adoption Impact to Balance Sheet (Details) - USD ($) $ in Millions	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net	$ 1,159	$ 1,198	$ 1,523
Contract assets	760	931	0
Other current assets	330	284	832
Deferred income taxes	945	982	1,023
Other assets	420	418	333
Contract liabilities	1,049	1,082	0
Accrued liabilities	1,096	1,187	2,286
Other liabilities	2,153	2,578	2,585
Retained earnings	627	594	467
Calculated under Revenue Guidance in Effect before Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net	1,364		1,523
Contract assets	0		0
Other current assets	821		832
Deferred income taxes	986		1,023
Other assets	328		333
Contract liabilities	0		0
Accrued liabilities	2,157		2,286
Other liabilities	2,163		2,585
Retained earnings	490		$ 467
Difference between Revenue Guidance in Effect before and after Topic 606 | Adjustments due to ASU 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net	205	(4)
Contract assets	(760)	85
Other current assets	491	(23)
Deferred income taxes	41	(41)
Other assets	(92)	85
Contract liabilities	(1,049)	(17)
Accrued liabilities	1,061	0
Other liabilities	10	(7)
Retained earnings	$ (137)	$ 127