Revenue Recognition (Narrative) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Contract with Customer, Asset and Liability [Abstract]
Beginning of period contract liability recorded as customer contract revenue during period	$ 5,340
Contract asset balance - current portion	1,729	$ 1,611
Contract liability balance - current portion	5,762	$ 5,939
Revenue, Performance Obligation [Abstract]
Aggregate amount of the transaction price allocated to remaining performance obligations	$ 39,385
Deferred Acquisition Costs | Minimum
Capitalized Contract Cost [Line Items]
Amortization period for deferred customer contract acquisition and fulfillment costs	3 years
Deferred Acquisition Costs | Maximum
Capitalized Contract Cost [Line Items]
Amortization period for deferred customer contract acquisition and fulfillment costs	5 years
Deferred Fulfillment Costs | Minimum
Capitalized Contract Cost [Line Items]
Amortization period for deferred customer contract acquisition and fulfillment costs	3 years
Deferred Fulfillment Costs | Maximum
Capitalized Contract Cost [Line Items]
Amortization period for deferred customer contract acquisition and fulfillment costs	5 years