Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Unbilled Audit Premiums	$ (27)	$ (27)	$ 4	$ (4)
Indefinite-lived Intangible Assets [Line Items]
Basic weighted average number of shares outstanding (in shares)		186,924	190,722	190,048
Deposit contracts, liabilities	38	$ 38	$ 41
Depreciation		53	54	$ 54
Interest payments		155	160	155
Income taxes paid		103	125	$ 186
Other Assets
Indefinite-lived Intangible Assets [Line Items]
Intangible assets, net (excluding goodwill)	$ 93	$ 93	$ 99
Grantor Trust \| Restricted Stock Units (RSUs)
Indefinite-lived Intangible Assets [Line Items]
Basic weighted average number of shares outstanding (in shares)	7,767,874

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Carrying amount of liabilities as of the balance sheet date pertaining to amounts received by the insurer or reinsurer from the insured (including a ceding company) under insurance or reinsurance contracts for which insurance risk is not transferred.

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Sum of the carrying amounts of all intangible assets, excluding goodwill, as of the balance sheet date, net of accumulated amortization and impairment charges.

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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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