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Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) shares in Thousands, $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Sep. 30, 2021 | Sep. 30, 2021 | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019 | Jan. 01, 2020
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |
Retained earnings |  |  | $ 9,663 | $ 9,081 |  |
Mortgage loans on real estate commercial and consumer allowance for credit loss |  |  | 16 | 26 |  |
Deferred income taxes |  |  | 142 | 66 |  |
Marketable securities fixed maturities allowance for credit loss |  |  | 18 | 40 |  |
Anticipated amounts due from insureds related to losses under deductible policies |  |  | $ 1,100 | $ 1,200 |  |
Structured settlement annuities, interest rate, low end |  |  | 6.40% |  |  |
Structured settlement annuities, interest rate, high end |  |  |  | 6.50% |  |
Discounted reserves for unfunded structured settlements |  |  | $ 503 | $ 520 |  |
Discounted reserves for unfunded structure settlements, discount amount |  |  | 621 | 657 |  |
Amount of interest recognized on the discounted reserves of unfunded structured settlements |  |  | $ 36 | $ 35 | $ 36 |
Interest rates at which workers' compensation lifetime claim reserves are discounted at |  |  | 3.50% | 3.50% |  |
Workers' compensation liability |  |  | $ 228 | $ 258 |  |
Discounted reserves for workers’ compensation lifetime claim reserves, discount amount |  |  | 97 | 113 |  |
Amount of interest accretion recognized on the discounted reserves of workers’ compensation lifetime claim reserves |  |  | $ 12 | $ 15 | $ 21 |
Long term care claim reserves weighted average discounted interest rate |  |  | 5.80% | 5.80% |  |
Discounted reserves for long term care claim reserves |  |  | $ 2,700 | $ 2,700 |  |
Premium deficiency |  |  | $ 428 | $ 439 |  |
Liability for future policy benefits, gross premium valuation, pretax margin | $ 72 | $ 72 |  |  |  |
Minimum interest rate used to calculate reserves for long term care products |  |  | 5.30% | 5.40% |  |
Liability balance for guaranty fund |  |  | $ 79 | $ 82 |  |
Percentage of billed receivables compared to total reinsurance receivable |  |  | 5.00% |  |  |
Policyholder dividends, rate on policy earnings |  |  | 1.00% | 1.00% | 1.00% |
Increase (decrease) in shadow adjustment, net of tax |  |  | $ (296) | $ 575 |  |
Reduction of net unrealized gains on investments included in AOCI due to shadow adjustments |  |  | 2,477 | 2,773 |  |
Foreign currency transaction gain (loss), before tax |  |  | $ (1) | $ 13 | $ 1 |
Operating lease, right-of-use asset, statement of financial position [Extensible List] |  |  | Other assets | Other assets |  |
Operating lease, liability, statement of financial position [Extensible List] |  |  | Other liabilities | Other liabilities |  |
Weighted average number diluted shares outstanding adjustment (in shares) |  |  | 1,000 | 770 | 960 |
Antidilutive securities excluded from computation of earnings per share, amount |  |  | 1 | 8 | 1 |
Interest paid, net |  |  | $ 110 | $ 124 | $ 136 |
Income taxes paid |  |  | $ 278 | $ 108 | $ 255 |
Furniture and Fixtures |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |
Property, plant and equipment, useful life |  |  | 7 years |  |  |
Office Equipment |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |
Property, plant and equipment, useful life |  |  | 5 years |  |  |
Computer Software, Intangible Asset |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |
Property, plant and equipment, useful life |  |  | 10 years |  |  |
Minimum |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |
Warranty coverage term |  |  | 1 month |  |  |
Requisite service period for stock- based compensation expense |  |  | 3 years |  |  |
Minimum | Computer Software, Intangible Asset |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |
Property, plant and equipment, useful life |  |  | 3 years |  |  |
Maximum |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |
Warranty coverage term |  |  | 10 years |  |  |
Maximum | Computer Software, Intangible Asset |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |
Property, plant and equipment, useful life |  |  | 5 years |  |  |
ASU 2016-13 |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |
Retained earnings |  |  |  |  |  | $ (5)
Mortgage loans on real estate commercial and consumer allowance for credit loss |  |  |  |  |  | 7
Deferred income taxes |  |  |  |  |  | 2
Marketable securities fixed maturities allowance for credit loss |  |  |  |  |  | $ 6
CNAF Consolidated | Loews |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |
Noncontrolling interest, ownership percentage by parent |  |  | 89.60% |  |  |

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