Earnings per share (Details) (USD $) In Millions, except Per Share data	3 Months Ended	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Numerator:
Net (loss) income	$ (620)	$ 145	$ (101)	$ 265
Denominator:
Weighted average common shares outstanding (in shares)	523.1	540.7	528.2	540.4
Effect of dilutive potential common shares:
Stock options (in shares)		2.1		2.0
Restricted stock units (non-participating) (in shares)		0.2
Weighted average common and dilutive potential common shares outstanding (in shares)	523.1	543.0	528.2	542.4
Earnings per share - Basic (in dollars per share)	$ (1.19)	$ 0.27	$ (0.19)	$ 0.49
Earnings per share - Diluted (in dollars per share)	$ (1.19)	$ 0.27	$ (0.19)	$ 0.49
Other Earnings Per Share Disclosures
Weighted average dilutive potential common shares outstanding resulting from stock options (in shares)	2.1		2.1
Weighted average dilutive potential common shares outstanding resulting from restricted stock options (in shares)	0.5		0.5
Weighted average common and dilutive potential common shares outstanding in the absence of the net loss (in shares)	525.7		530.8
Antidilutive stock options, exercise price exceeds market price (in shares)	28.3	27.3	28.4	26.1
Antidilutive stock options, exercise price exceeds market price, exercise price range, low end of range (in dollars per share)	$ 27.36	$ 28.52	$ 27.36	$ 27.36
Antidilutive stock options, exercise price exceeds market price, exercise price range, high end of range (in dollars per share)	$ 62.84	$ 62.84	$ 62.84	$ 64.53

The high end of the range of specified exercise prices for stock options with exercise prices exceeding the average market price of common shares during the period or for which the unrecognized compensation cost would have an anti-dilutive effect.

Name:	all_AntidilutiveSecuritiesExcludedFromComputationOfEarningPerShareExercisePriceRangeHigher
Namespace Prefix:	all
Data Type:	us-types:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

The low end of the range of specified exercise prices for stock options with exercise prices exceeding the average market price of common shares during the period or for which the unrecognized compensation cost would have an anti-dilutive effect.

+ Details

Name:	all_AntidilutiveSecuritiesExcludedFromComputationOfEarningPerShareExercisePriceRangeLower
Namespace Prefix:	all
Data Type:	us-types:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of restricted shares from share-based payment arrangements with an anti-dilutive effect on earnings per share because the entity reported a net loss during the period. These securities were not included in the computation of diluted EPS because to do so would increase EPS amounts or decrease loss per share amounts for the period presented.

+ Details

Name:	all_AntidilutiveSecuritiesShareBasedPaymentArrangementsResultingFromNetLossRestrictedShares
Namespace Prefix:	all
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of shares from share-based payment arrangements with an anti-dilutive effect on earnings per share because the entity reported a net loss during the period. These securities were not included in the computation of diluted EPS because to do so would increase EPS amounts or decrease loss per share amounts for the period presented.

+ Details

Name:	all_AntidilutiveSecuritiesShareBasedPaymentArrangementsResultingFromNetLossShares
Namespace Prefix:	all
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	all_DenominatorAbstract
Namespace Prefix:	all
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Aggregate awards of share options to be issued to an employee under a share-based compensation arrangement considered for purposes of computing diluted earnings per share.

+ Details

Name:	all_IncrementalCommonSharesAttributableToEmployeeStockOptions
Namespace Prefix:	all
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Aggregate awards of restricted stock to be issued to an employee under a share-based compensation arrangement considered for purposes of computing diluted earnings per share.

+ Details

Name:	all_IncrementalCommonSharesAttributableToRestrictedStockUnits
Namespace Prefix:	all
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	all_NumeratorAbstract
Namespace Prefix:	all
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	all_OtherEarningsPerShareDisclosuresAbstract
Namespace Prefix:	all
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The average number of shares issued and outstanding that would have been used in calculating diluted EPS, if the entity had not reported a net loss for the period.

+ Details

Name:	all_WeightedAverageNumberOfDilutedSharesOutstandingInAbsenceOfNetLoss
Namespace Prefix:	all
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) in the future that were not included in the computation of diluted EPS because to do so would increase EPS amounts or decrease loss per share amounts for the period presented.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 13, 14

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 171

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 40
-Subparagraph c

+ Details

Name:	us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
Namespace Prefix:	us-gaap
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_DilutiveSecuritiesAbstract
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of net income or loss for the period per each share of common stock outstanding during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Paragraph 21
-Article 9

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 36, 37, 38

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 20
-Article 5

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Paragraph 18
-Article 7

+ Details

Name:	us-gaap_EarningsPerShareBasic
Namespace Prefix:	us-gaap
Data Type:	us-types:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of net income or loss for the period per each share of common stock and dilutive common stock equivalents outstanding during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 11, 12, 36

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 20
-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Paragraph 18
-Article 7

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Paragraph 21
-Article 9

+ Details

Name:	us-gaap_EarningsPerShareDiluted
Namespace Prefix:	us-gaap
Data Type:	us-types:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Research Bulletin (ARB)
-Number 51
-Paragraph A1, A4, A5

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Research Bulletin (ARB)
-Number 51
-Paragraph 5
-Subparagraph b

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Research Bulletin (ARB)
-Number 51
-Paragraph 29

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Research Bulletin (ARB)
-Number 51
-Paragraph 38
-Subparagraph a

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Research Bulletin (ARB)
-Number 51
-Paragraph 38
-Subparagraph c(1)

+ Details

Name:	us-gaap_ProfitLoss
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The average number of shares issued and outstanding that are used in calculating diluted EPS, determined based on the timing of issuance of shares in the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 40
-Subparagraph a

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 8

+ Details

Name:	us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding
Namespace Prefix:	us-gaap
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 171

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 40
-Subparagraph a

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 8

+ Details

Name:	us-gaap_WeightedAverageNumberOfSharesOutstandingBasic
Namespace Prefix:	us-gaap
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration