Insurance - Recoverables from reinsurance, progression of allowance for expected credit losses (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020	Jan. 01, 2020
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	$ 6	$ 18
Impact of adoption of new accounting principles	(7)	(7)	$ (11)
Provision (credit) for expected credit losses	1	0
Write-offs charged against the allowance	0	0
Ending Balance	$ 7	$ 7

Amount of the write-down or write-off of a receivable from a reinsurer.

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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- Definition

Amount of expense (reversal of expense) for expected credit loss on reinsurance recoverable.

+ References

+ Details

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

- Definition

Amount of allowance for credit loss on reinsurance recoverable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121599878&loc=SL82895884-210446

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant