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Principles of Consolidation And Other Matters (Details) - USD ($) | 3 Months Ended | 6 Months Ended |  |
--- | --- | --- | --- | ---
Jun. 30, 2019 | Jun. 30, 2018 | Jun. 30, 2019 | Jun. 30, 2018 | Jan. 01, 2019 | Dec. 31, 2018
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items] |  |  |  |  |  |
Operating funds related to regulatory requirements or as collateral under captive insurance arrangements | $ 192,000,000 |  | $ 192,000,000 |  |  | $ 186,000,000
Equity method investments lag period |  |  | 3 months |  |  |
Gain (loss) on investment income, net | 8,000,000 | $ 28,000,000 | $ 13,000,000 | $ 28,000,000 |  |
Gains on equity investments | 3,000,000 | 26,000,000 | 6,000,000 | 19,000,000 |  |
Equity method income | 5,000,000 | $ 2,000,000 | 7,000,000 | $ 9,000,000 |  |
Operating lease, liability | 2,328,000,000 |  | 2,328,000,000 |  |  |
Operating lease, right-of-use asset | $ 2,016,000,000 |  | $ 2,016,000,000 |  |  | 0
Effective tax rate (as a percent) | 37.40% | 25.60% | 28.20% | 24.70% |  |
Unrecognized tax benefits | $ 74,000,000 |  | $ 74,000,000 |  |  | $ 78,000,000
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 | $ 10,000,000 |  | $ 10,000,000 |  |  |
Accounting Standards Update 2016-02 |  |  |  |  |  |
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items] |  |  |  |  |  |
Operating lease, liability |  |  |  |  | $ 1,900,000,000 |
Operating lease, right-of-use asset |  |  |  |  | 1,700,000,000 |
Restatement Adjustment | Accounting Standards Update 2016-02 |  |  |  |  |  |
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items] |  |  |  |  |  |
Other liabilities |  |  |  |  | $ 200,000,000 |

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