Shareholders' Equity - Number of Shares Issued and Outstanding and Carrying Amount of Preferred Stock (Detail) (USD $) In Millions, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Class of Stock [Line Items]
Shares Issued and Outstanding	159,910us-gaap_PreferredStockSharesOutstanding	159,910us-gaap_PreferredStockSharesOutstanding
Liquidation Preference	$ 4,936	$ 4,936
Discount	180us-gaap_PreferredStockDiscountOnShares	180us-gaap_PreferredStockDiscountOnShares
Carrying Amount	4,756	4,756
Series A [Member]
Class of Stock [Line Items]
Shares Issued and Outstanding	12,510	12,510
Liquidation Preference	1,251	1,251
Discount	145	145
Carrying Amount	1,106	1,106
Series B [Member]
Class of Stock [Line Items]
Shares Issued and Outstanding	40,000	40,000
Liquidation Preference	1,000	1,000
Carrying Amount	1,000	1,000
Series F [Member]
Class of Stock [Line Items]
Shares Issued and Outstanding	44,000	44,000
Liquidation Preference	1,100	1,100
Discount	12	12
Carrying Amount	1,088	1,088
Series G [Member]
Class of Stock [Line Items]
Shares Issued and Outstanding	43,400	43,400
Liquidation Preference	1,085	1,085
Discount	10	10
Carrying Amount	1,075	1,075
Series H [Member]
Class of Stock [Line Items]
Shares Issued and Outstanding	20,000	20,000
Liquidation Preference	500	500
Discount	13	13
Carrying Amount	$ 487	$ 487

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Discount on preferred shares, or any unamortized balance thereof, shown separately as a deduction from the applicable account(s) as circumstances require.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 7

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187103-122770

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- Definition

Aggregate par value plus amounts in excess of par or issuance value (in cases of no-par value stock) for nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) issued and outstanding, net of discount on shares. Aggregate for preferred stock issued and outstanding.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.4-07)

-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187103-122770

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 7

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.28,30(a))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Value of the difference between preference in liquidation and the par or stated values of the preferred shares.

+ References

No definition available.

+ Details

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- Definition

Aggregate share number for all nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) held by stockholders. Does not include preferred shares that have been repurchased.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.28)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 29

-Article 5

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