Derivative Financial Instruments - Fair value of instruments with credit-risk-contingent features (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Gross liability fair value of contracts containing credit-risk-contingent features	$ 38	$ 28
Gross asset fair value of contracts containing credit-risk-contingent features and subject to MNAs	(33)	(17)
Collateral posted under MNAs for contracts containing credit-risk-contingent features	(4)	(6)
Maximum amount of additional exposure for contracts with credit-risk-contingent features if all features were triggered concurrently	$ 1	$ 5

Fair value of derivative asset, presented on a gross basis containing credit risk contingent features and which is subject to master netting arrangements.

No definition available.

+ Details

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Balance Type:	debit
Period Type:	instant

- Definition

Fair value of derivative liabilities, presented on a gross basis containing credit risk contingent features.

+ References

No definition available.

+ Details

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Namespace Prefix:	all_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

- Definition

The aggregate fair value of additional assets that would be required to be posted as collateral for derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624258-113959

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Balance Type:	debit
Period Type:	instant

- Definition

The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624258-113959

+ Details

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

- References

No definition available.

+ Details

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