Securities - Amortized Cost, Gross Unrealized Gains, Gross Unrealized Losses, and Fair Values of Securities (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 23,897	$ 21,076
Gross Unrealized Gains	157	414
Gross Unrealized Losses	544	138
Fair Value	23,510	21,352
U.S. government sponsored agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	362	866
Gross Unrealized Gains	2	19
Fair Value	364	885
U.S. government agency and government sponsored agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	14,930	13,104
Gross Unrealized Gains	57	232
Gross Unrealized Losses	314	3
Fair Value	14,673	13,333
Privately issued [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	330	445
Gross Unrealized Gains	4	8
Gross Unrealized Losses	6	10
Fair Value	328	443
Commercial mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,904	2,863
Gross Unrealized Gains	24	114
Gross Unrealized Losses	178	6
Fair Value	3,750	2,971
Collateralized loan obligations (CLOs) [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,414	1,996
Gross Unrealized Gains	33	7
Gross Unrealized Losses	2	44
Fair Value	2,445	1,959
Asset-backed and other [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	79	145
Gross Unrealized Gains	1	1
Fair Value	80	146
Asset Liability Management securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	22,019	19,419
Gross Unrealized Gains	121	381
Gross Unrealized Losses	500	63
Fair Value	21,640	19,737
Direct bank purchase bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,708	1,482
Gross Unrealized Gains	33	27
Gross Unrealized Losses	38	71
Fair Value	1,703	1,438
Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	155	156
Gross Unrealized Gains	3	6
Gross Unrealized Losses	6	4
Fair Value	152	158
Equity securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	15	19
Fair Value	$ 15	$ 19

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 1

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

-Publisher FASB

-Name Accounting Standards Codification

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 12

-Subparagraph 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 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 16

-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 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 14

-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 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 13

-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 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 22

-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 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

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-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 9: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15E

-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 10: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15C

-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.

+ Details

- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

+ References+ Details