Revenue Recognition - Deferred Contract Costs (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017	[1]
Deferred Contract Costs
Deferred contract costs	$ 4,808
Deferred contract costs, current	2,227		$ 1,820
Deferred contract costs, noncurrent	2,581		$ 2,136
Amortization of deferred contract costs	929
Impairment of deferred contract costs
Accounting Standards Update 2014-09, Revenue from Contracts with Customers | Adjustments for adoption of guidance
Deferred Contract Costs
Deferred contract costs		$ 737
Costs to obtain a contract
Deferred Contract Costs
Deferred contract costs	681
Deferred setup costs
Deferred Contract Costs
Deferred contract costs	2,123
Other deferred fulfillment costs
Deferred Contract Costs
Deferred contract costs	$ 2,003

[1] Recast to conform to current period presentation.