Other Commitments And Other Operating Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Commitments And Contingencies [Abstract]
2018	$ 44
2019	41
2020	40
2021	36
2022	27
Thereafter	138
Total	326
Payments for other commitments and operating leases	$ 45	$ 43	$ 41
Property Subject To Or Available For Operating Lease Expiration Beginning Date	2018
Property Subject To Or Available For Operating Lease Expiration Ending Date	2052