Contingencies - Narrative (Details) $ in Millions	9 Months Ended
Sep. 30, 2021 USD ($) vehicle
Commitments and Contingencies Disclosure [Abstract]
Reductions in premiums written, net \| $	$ 128
Number of vehicle, individual policies, mileage reduction \| vehicle	310,000

Amount, after premiums ceded to other entities and premiums assumed by the entity, of decrease (increase) in unearned premiums.

No definition available.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration