Revenues and Contract Costs - Contract with Customer, Asset and Liability (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018
Change in Contract with Customer, Assets [Roll Forward]
Beginning balance		$ 1,170
Increase resulting from new contracts		1,183
Contract assets reclassified to a receivable or collected in cash		(1,208)
Other		(148)
Ending balance	$ 997	997
Change in Contract with Customer, Liabilities [Roll Forward]
Beginning balance		4,452
Net increase in contract liabilities		4,144
Revenue recognized from previously recognized contract liability	100	(3,881)
Other		(22)
Ending balance	4,693	4,693
Prepaid expenses and other
Change in Contract with Customer, Assets [Roll Forward]
Ending balance	753	753
Other assets
Change in Contract with Customer, Assets [Roll Forward]
Ending balance	244	244
Other current liabilities
Change in Contract with Customer, Liabilities [Roll Forward]
Ending balance	4,000	4,000
Other liabilities
Change in Contract with Customer, Liabilities [Roll Forward]
Ending balance	$ 693	693
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