Revision of Previously Issued Financial Statements (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		15 Months Ended	48 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Mar. 31, 2017	Mar. 31, 2017
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of sales	$ 1,946	$ 1,816	$ 3,877	$ 3,586
Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of sales		$ 6		$ 6
Lump Sum Payments Immediately Recognized, Should Have Been Deferred And Amortized | Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of sales					$ 7	$ 34
Deferred charges	$ 27		$ 27