Revenue Recognition (Narrative) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Contract with Customer, Asset and Liability [Abstract]
Beginning of period contract liability recorded as customer contract revenue during period	$ 5,295
Contract asset balance - current portion (in millions)	1,496	$ 1,244
Contract liability balance - current portion (in millions)	5,910	$ 5,752
Revenue, Performance Obligation [Abstract]
Aggregate amount of the transaction price allocated to remaining performance obligations (in millions)	$ 40,216
Aggregate amount of the transaction price allocated to remaining performance obligations (percentage)	70.00%
Deferred Customer Contract Acquisition Costs [Member]
Capitalized Contract Cost [Line Items]
Capitalized Contract Cost, Amortization Method	For contracts with an estimated amortization period of less than one year, we expense incremental costs immediately.
Deferred Customer Contract Acquisition Costs [Member] | Minimum [Member]
Capitalized Contract Cost [Line Items]
Capitalized Contract Cost, Amortization Period	3 years
Deferred Customer Contract Acquisition Costs [Member] | Maximum [Member]
Capitalized Contract Cost [Line Items]
Capitalized Contract Cost, Amortization Period	5 years
Deferred Customer Contract Fulfillment Cost [Member]
Capitalized Contract Cost [Line Items]
Capitalized Contract Cost, Amortization Method	For contracts with an estimated amortization period of less than one year, we expense incremental costs immediately.
Deferred Customer Contract Fulfillment Cost [Member] | Minimum [Member]
Capitalized Contract Cost [Line Items]
Capitalized Contract Cost, Amortization Period	3 years
Deferred Customer Contract Fulfillment Cost [Member] | Maximum [Member]
Capitalized Contract Cost [Line Items]
Capitalized Contract Cost, Amortization Period	5 years