Accumulated Other Comprehensive Income - Adjustments to Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Class of Stock [Line Items]
Net interest revenue	$ 546us-gaap_InterestIncomeExpenseNet	$ 555us-gaap_InterestIncomeExpenseNet
Total reclassifications out of AOCI	377	356
Reclassification out of Accumulated Other Comprehensive Income
Class of Stock [Line Items]
Total reclassifications out of AOCI	5	(3)
Net Unrealized Gains (Losses) on Cash Flow Hedges \| Interest-rate contracts \| Reclassification out of Accumulated Other Comprehensive Income
Class of Stock [Line Items]
Net interest revenue	1	1
Net Unrealized Gains (Losses) on Available-for-Sale Securities \| Reclassification out of Accumulated Other Comprehensive Income
Class of Stock [Line Items]
Net gains (losses) from sales of available-for-sale securities	0	(9)
Gain (Loss) on Investments, Excluding Other than Temporary Impairments, Tax	0	(6)
Other-Than-Temporary Impairment on Held-to-Maturity Securities \| Reclassification out of Accumulated Other Comprehensive Income
Class of Stock [Line Items]
Other-than-temporary impairment on held-to-maturity securities related to factors other than credit	(1)	0
Net Unrealized Losses on Retirement Plans \| Reclassification out of Accumulated Other Comprehensive Income
Class of Stock [Line Items]
Amortization of actuarial losses, net of related tax benefits of $3 and $3, respectively	5	5
OCI reclassification adjustment, pension and other postretirement benefit plans, tax	$ (4)	$ 3

Gain (Loss) on Investments, Excluding Other than Temporary Impairments, Tax

No definition available.

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- Definition

This item represents the net total realized and unrealized gain (loss) included in earnings for the period as a result of selling or holding marketable securities categorized as trading, available-for-sale, or held-to-maturity, including the unrealized holding gain (loss) of held-to-maturity securities transferred to the trading security category and the cumulative unrealized gain (loss) which was included in other comprehensive income (a separate component of shareholders' equity) for available-for-sale securities transferred to trading securities during the period. Additionally, this item would include any gains (losses) realized during the period from the sale of investments accounted for under the cost method of accounting.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 7

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph ((b)(7))

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- Definition

The net amount of operating interest income (expense).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.10)

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 10

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Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 260

-SubTopic 10

-Section 45

-Paragraph 11

-URI http://asc.fasb.org/extlink&oid=7655603&loc=d3e1377-109256

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- Definition

Amount before tax of reclassification adjustment from accumulated other comprehensive income (loss) for actuarial gain (loss) related to pension and other postretirement benefit plans.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 11

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (i)

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-Topic 220

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-Section 45

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- Definition

Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income (loss) for actuarial gain (loss) related to pension and other postretirement benefit plans.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 15

-URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e689-108580

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- Definition

The amount of other than temporary impairment losses on investments in debt securities categorized as Held-to-maturity which have been recognized in earnings during the period. Such impairment losses consist of other than temporary impairments (OTTI) of investments in debt securities due to credit losses and other than temporary impairments due to other than credit losses when the entity intends to sell an impaired debt security or it is more likely than not that the entity will be required to sell the impaired debt security before recovery of its amortized cost basis.

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-Name Accounting Standards Codification

-Topic 320

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-Section 50

-Paragraph 5

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