Goodwill and Other Intangible Assets (Other Intangible Assets) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Net Amount	$ 798	$ 742
Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Weighted-Average Remaining Amortization Period	29 months	28 months
Gross Carrying Amount	$ 67	$ 70
Accumulated Amortization	59	57
Net Amount	$ 8	$ 13
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Weighted-Average Remaining Amortization Period	9 years	10 years
Gross Carrying Amount	$ 1,585	$ 1,465
Accumulated Amortization	795	737
Net Amount	$ 790	$ 728
Trade names and associated trademarks
Finite-Lived Intangible Assets [Line Items]
Weighted-Average Remaining Amortization Period		4 months
Gross Carrying Amount		$ 80
Accumulated Amortization		79
Net Amount		$ 1