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Schedule I - Summary Of Investments (Details) - USD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019
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SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties, Cost | $ 2,847 |
Investments | 3,028 |
Available-for-sale Securities, Amortized Cost Basis | 2,807 |
Other Investments | 595 | $ 478
Available-for-sale Securities | 2,949 | 3,314
Investments | 3,544 | 3,792
Short-term Investments [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Available-for-sale Securities, Amortized Cost Basis | 492 |
Available-for-sale Securities | 492 |
ShortTermInvestmentsMember, including Pledged |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Available-for-sale Securities, Amortized Cost Basis | 617 |
Available-for-sale Securities | 617 |
Fixed Income Securities [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Available-for-sale Securities, Amortized Cost Basis | 2,175 |
Available-for-sale Securities | 2,317 | 2,577
Fixed Income Securities [Member] | Municipal Bonds [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Available-for-sale Securities, Amortized Cost Basis | 321 |
Available-for-sale Securities | 358 | 215
Fixed Income Securities [Member] | Corporate Debt Securities [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Available-for-sale Securities, Amortized Cost Basis | 1,059 |
Available-for-sale Securities | 1,077 | 1,430
Fixed Income Securities [Member] | Debt Security, Government, Non-US [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Available-for-sale Securities, Amortized Cost Basis | 97 |
Available-for-sale Securities | 98 | 44
Fixed Income Securities [Member] | Residential Mortgage-Backed Securities [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Available-for-sale Securities, Amortized Cost Basis | 256 |
Available-for-sale Securities | 302 | 248
Fixed Income Securities [Member] | Collateralized Debt Obligations [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Available-for-sale Securities, Amortized Cost Basis | 74 |
Available-for-sale Securities | 74 | 146
Fixed Income Securities [Member] | Asset-backed Securities [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Available-for-sale Securities, Amortized Cost Basis | 263 |
Available-for-sale Securities | 303 | 287
Fixed Income Securities [Member] | Short-term Investments [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Available-for-sale Securities |  | 653
Fixed Income Securities [Member] | U S Government Obligations [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Available-for-sale Securities, Amortized Cost Basis | 120 |
Available-for-sale Securities | 121 |
Fixed Income Securities [Member] | US Government Debt Securities [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Available-for-sale Securities, Amortized Cost Basis | 105 |
Available-for-sale Securities | 106 | $ 156
Fixed Income Securities [Member] | Corporate Obligations, Excluding Related Party Investments |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Available-for-sale Securities, Amortized Cost Basis | 592 |
Available-for-sale Securities | 612 |
Fair Value Amount, Excluding Related Party Investments [Domain] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Investments | $ 3,028 |

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