Income Taxes - Continuing Operations (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Tax Disclosure [Abstract]
Provision (benefit) for income taxes	$ 338	$ 227	$ 439
Income taxes related to adjustments included in common shareholder’s equity:
Unrealized gains (losses) on securities available-for-sale, net	76	552	96
Unrealized gains (losses) on derivatives classified as cash flow hedges	17	(110)	10
Employer accounting for post-retirement plans	5	(3)	(2)
Other-than-temporary impairment	0	1	30
Total	$ 436	$ 667	$ 573

Income Tax Expense (Benefit), Intraperiod Tax Allocation, Excluding Discontinued Operations

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- Definition

Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Classified as Cash Flow Hedges Arising During Period, Tax

+ References

No definition available.

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- Definition

Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Available-For-Sale Securities Arising During Period, Tax

+ References

No definition available.

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- Definition

The sum of the current income tax expense or benefit and the deferred income tax expense or benefit pertaining to continuing operations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 9

-Subparagraph (a),(b)

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 109

-Paragraph 45

-Subparagraph a, b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(h))

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 08

-Paragraph h

-Article 4

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Income Tax Expense (or Benefit)

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- Definition

Tax effect, net of reclassification adjustments, of pension and other postretirement benefit plans (gain) loss included in accumulated other comprehensive income (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 12

-URI http://asc.fasb.org/extlink&oid=20435746&loc=d3e640-108580

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 10A

-Subparagraph (i-k)

-URI http://asc.fasb.org/extlink&oid=20435746&loc=SL7669646-108580

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- Definition

Tax effect of other than temporary impairment (OTTI) on a debt security, categorized as available-for-sale or held-to-maturity, recognized in other comprehensive income (loss), attributable to the parent entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15D

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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