Accounting Polices Related to Revenue from Contracts with Customers Contract with Customer, Asset and Liability (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Change in Contract with Customer, Asset and Liability [Abstract]
Contract with Customer, Asset, Net	$ 22	$ 22	$ 28
Contract liabilities	469	469	458
Contract with Customer, Liability, Noncurrent	$ 90	90	$ 95
Contract with Customer, Liability, Revenue Recognized		$ 266
Fees Related to Software Application, Contract Term	5 years
Incremental and Recoverable Contract-Specific Costs, Amortization Period	7 years