Revenues and Contract Costs - Contract with Customer, Asset and Liability (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018
Change in Contract with Customer, Assets [Roll Forward]
Beginning balance		$ 1,170
Increase resulting from new contracts		824
Contract assets reclassified to a receivable or collected in cash		(824)
Other		(111)
Ending balance	$ 1,059	1,059
Change in Contract with Customer, Liabilities [Roll Forward]
Beginning balance		4,452
Net increase in contract liabilities		3,998
Revenue recognized from previously recognized contract liability	(300)	(3,780)
Other		(18)
Ending balance	4,652	4,652
Prepaid expenses and other
Change in Contract with Customer, Assets [Roll Forward]
Ending balance	776	776
Other assets
Change in Contract with Customer, Assets [Roll Forward]
Ending balance	283	283
Other current liabilities
Change in Contract with Customer, Liabilities [Roll Forward]
Ending balance	4,006	4,006
Other liabilities
Change in Contract with Customer, Liabilities [Roll Forward]
Ending balance	$ 646	646
Adjustments | Accounting Standards Update 2014-09
Change in Contract with Customer, Assets [Roll Forward]
Beginning balance		1,132
Change in Contract with Customer, Liabilities [Roll Forward]
Beginning balance		(634)
Balances without adoption of Topic 606 | Accounting Standards Update 2014-09
Change in Contract with Customer, Assets [Roll Forward]
Beginning balance		38
Change in Contract with Customer, Liabilities [Roll Forward]
Beginning balance		$ 5,086