Principles of Consolidation And Other Matters (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Operating funds related to regulatory requirements or as collateral under captive insurance arrangements	$ 172,000,000		$ 172,000,000
Equity method investments lag period			3 months
Investment income (loss)	$ 5,000,000	$ 1,000,000	$ 5,000,000	$ (2,000,000)
Effective tax rate (as a percent)	28.60%	29.50%	25.90%	29.00%
Unrecognized tax benefits	$ 66,000,000		$ 66,000,000		$ 65,000,000
Minimum
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Reasonably possible decrease in unrecognized tax benefits	0		0
Maximum
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Reasonably possible decrease in unrecognized tax benefits	$ 9,000,000		$ 9,000,000