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Principles of Consolidation And Other Matters (Details) - USD ($) | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2017 | Sep. 30, 2016 | Sep. 30, 2017 | Sep. 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 | $ 184,000,000 |  | $ 184,000,000 |  |
Equity method investments lag period |  |  | 3 months |  |
Investment income |  | $ 1,000,000 | $ 3,000,000 |  |
Investment loss | $ (2,000,000) |  |  | $ (2,000,000) |
Effective tax rate (as a percent) | 26.20% | 26.80% | 25.90% | 28.40% |
Unrecognized tax benefits | $ 64,000,000 |  | $ 64,000,000 |  | $ 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 |  |

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