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Business Developments And Risks And Uncertainties (Narrative) (Detail) $ in Millions |  |  | 3 Months Ended
--- | --- | --- | ---
Feb. 10, 2021 USD ($) | Jan. 01, 2021 USD ($) | Mar. 31, 2021 USD ($) segments
Business Acquisition [Line Items] |  |  |
Number of operating segments | segments |  |  | 3
Federal legislation passed to combat the economic impact |  |  | $ 2,700,000
New relief plan proposed to stabilize the financial system |  |  | 1,900,000
Aid allocated to state and local governments |  |  | 350,000
Credit Suisse [Member] |  |  |
Business Acquisition [Line Items] |  |  |
Damages Paid Value | $ 600 |  |
Damages Sought Value |  |  | 604
Puerto Rico [Member] |  |  |
Business Acquisition [Line Items] |  |  |
Claims payments |  | $ 51 |
Outstanding bonds |  |  | 2,900
MBIA Corp Financing Facility [Member] |  |  |
Business Acquisition [Line Items] |  |  |
Payment for Debt Extinguishment or Debt Prepayment Cost |  |  | $ 150
Debt Instrument, Interest Rate, Stated Percentage |  |  | 12.00%
Debt Instrument, Maturity Date |  |  | Jan. 20, 2022
Long-term Debt |  |  | $ 127

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