Accounting Polices Related to Revenue from Contracts with Customers Contract with Customer, Asset and Liability (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Change in Contract with Customer, Asset and Liability [Abstract]
Contract with Customer, Asset, Net	$ 23	$ 28
Contract liabilities	538	458
Contract with Customer, Liability, Noncurrent	95	$ 95
Contract with Customer, Liability, Revenue Recognized	$ 199
Fees Related to Software Application, Contract Term	5 years
Incremental and Recoverable Contract-Specific Costs, Amortization Period	7 years