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Principles of Consolidation And Other Matters (Details) | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2018 USD ($) | Dec. 31, 2017 USD ($) discrete_charge | Sep. 30, 2017 USD ($) | Sep. 30, 2018 USD ($) | Sep. 30, 2017 USD ($) | Jan. 01, 2018 USD ($)
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items] |  |  |  |  |  |
Operating funds related to regulatory requirements or as collateral under captive insurance arrangements | $ 189,000,000 |  |  | $ 189,000,000 |  |
Equity method investments lag period |  |  |  | 3 months |  |
Gain (loss) on investment income, net | (52,000,000) |  | $ (2,000,000) | $ (24,000,000) | $ 3,000,000 |
Equity method investment, other than temporary impairment |  |  |  | 81,000,000 |  |
Gains on equity investments | 25,000,000 |  |  | 43,000,000 |  |
Equity method income | $ 4,000,000 |  |  | $ 14,000,000 |  |
Effective tax rate (as a percent) | 27.50% |  | 26.20% | 25.20% | 25.90% |
Number of discrete charges | discrete_charge |  | 2 |  |  |  |
Period for payable on undistributed earnings |  |  |  | 8 years |  |
Provisional income tax expense (benefit) |  |  |  | $ 240,000,000 |  |
Transition tax for accumulated foreign earnings, liability | $ 3,400,000,000 |  |  | 3,400,000,000 |  |
Provisional withholding and state income tax expense (benefit) | 226,000,000 |  |  | 53,000,000 |  |
Change in tax rate, deferred tax asset, provisional income tax expense (benefit) |  |  |  | 220,000,000 |  |
Decrease to income tax expense (benefit) |  |  |  | 14,000,000 |  |
Increase to income tax expense (benefit) |  |  |  | 3,000,000 |  |
Unrecognized tax benefits | 72,000,000 | $ 71,000,000 |  | 72,000,000 |  |
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 |  |
Retained Earnings |  |  |  |  |  |
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items] |  |  |  |  |  |
Cumulative effect of new accounting principle in period of adoption |  | $ 14,000,000 |  |  |  | $ 14,000,000

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