Revenues and Contract Costs - Contract with Customer, Asset and Liability (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jan. 01, 2020	Dec. 31, 2019	Jan. 01, 2019
Disaggregation of Revenue [Line Items]
Contract asset	$ 923	$ 1,102	$ 923	$ 1,102	$ 1,150	$ 1,150	$ 1,003
Contract liability	5,321	5,082	5,321	5,082	$ 5,307	5,307	$ 4,943
Revenue recognized related to contract liabilities existing	124	$ 235	4,200	$ 4,100
Prepaid expenses and other
Disaggregation of Revenue [Line Items]
Contract asset	733		733			848
Other assets
Disaggregation of Revenue [Line Items]
Contract asset	190		190			302
Other current liabilities
Disaggregation of Revenue [Line Items]
Contract liability	4,683		4,683			4,651
Other liabilities
Disaggregation of Revenue [Line Items]
Contract liability	$ 638		$ 638			$ 656