Goodwill and Other Intangible Assets (Other Intangible Assets) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Net Amount	$ 895	$ 875
Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Weighted-Average Remaining Amortization Period	28 months	31 months
Gross Carrying Amount	$ 23	$ 71
Accumulated Amortization	17	62
Net Amount	$ 6	$ 9
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Weighted-Average Remaining Amortization Period	8 years	9 years
Gross Carrying Amount	$ 1,897	$ 1,750
Accumulated Amortization	1,013	884
Net Amount	$ 884	$ 866
Trade names and associated trademarks
Finite-Lived Intangible Assets [Line Items]
Weighted-Average Remaining Amortization Period	5 years
Gross Carrying Amount	$ 5
Accumulated Amortization	0
Net Amount	$ 5