| **Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Millions, $ in Millions** | Mar. 31, 2022 | Dec. 31, 2021 |
|-------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Statement of Financial Position [Abstract]**                                                        |          |          |
| Debt Securities, Available-for-sale, Amortized Cost                                                   | $ 12,330      | $ 12,230      |
| Equity Securities, FV-NI, Cost                                                                        | 4,167         | 4,121         |
| Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment                  | $ 309         | $ 303         |
| Common Stock, Par or Stated Value Per Share                                                           | $ 2           | $ 2           |
| Common Stock, Shares Authorized                                                                       | 500.0         | 500.0         |
| Common Stock, Shares, Issued                                                                          | 198.3         | 198.3         |
| Treasury Stock, Shares                                                                                | 38.0          | 38.0          |

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|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
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| - Definition
Face amount or stated value per share of common stock.
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| - Definition
The maximum number of common shares permitted to be issued by an entity's charter and bylaws.
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.
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| - Definition
Cost of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). Excludes equity method investment and investment in equity security without readily determinable fair value.
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| - Definition
Number of common and preferred shares that were previously issued and that were repurchased by the issuing entity and held in treasury on the financial statement date. This stock has no voting rights and receives no dividends.
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