Fair Value Measurements (Carrying Values And Fair Values Of Financial Instruments Not Measured At Fair Value) (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Document Period End Date	Dec. 31, 2015
Held-to-maturity Securities, Fair Value	$ 8,552	$ 7,589
Repurchase agreements	1,404	1,402
Financial Instruments Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity Securities, Fair Value	8,552	7,589
Repurchase agreements	1,404	1,402
Short-term debt		1,169
Long-term debt	9,678	3,690
Trust preferred securities	446	462
Total liabilities	11,528	6,723
Financial Instruments Fair Value [Member] \| U.S. Treasury and agency
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity Securities, Fair Value	745	850
Financial Instruments Fair Value [Member] \| Foreign
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity Securities, Fair Value	785	963
Financial Instruments Fair Value [Member] \| Corporate Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity Securities, Fair Value	3,056	2,423
Financial Instruments Fair Value [Member] \| Mortgage backed-securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity Securities, Fair Value	1,743	2,039
Financial Instruments Fair Value [Member] \| US States and Political Subdivisions Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity Securities, Fair Value	2,223	1,314
Level 2 \| Financial Instruments Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity Securities, Fair Value	7,955	6,915
Repurchase agreements	1,404	1,402
Short-term debt		1,169
Long-term debt	9,678	3,690
Trust preferred securities	446	462
Total liabilities	11,528	6,723
Level 2 \| Financial Instruments Fair Value [Member] \| U.S. Treasury and agency
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity Securities, Fair Value	162	191
Level 2 \| Financial Instruments Fair Value [Member] \| Foreign
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity Securities, Fair Value	785	963
Level 2 \| Financial Instruments Fair Value [Member] \| Corporate Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity Securities, Fair Value	3,042	2,408
Level 2 \| Financial Instruments Fair Value [Member] \| Mortgage backed-securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity Securities, Fair Value	1,743	2,039
Level 2 \| Financial Instruments Fair Value [Member] \| US States and Political Subdivisions Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity Securities, Fair Value	2,223	1,314
Level 3 \| Securities Loaned or Sold under Agreements to Repurchase [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Repurchase agreements		0
Level 3 \| Financial Instruments Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity Securities, Fair Value	14	15
Short-term debt		0
Long-term debt		0
Trust preferred securities		0
Total liabilities		0
Level 3 \| Financial Instruments Fair Value [Member] \| U.S. Treasury and agency
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity Securities, Fair Value	0	0
Level 3 \| Financial Instruments Fair Value [Member] \| Foreign
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity Securities, Fair Value		0
Level 3 \| Financial Instruments Fair Value [Member] \| Corporate Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity Securities, Fair Value	14	15
Level 3 \| Financial Instruments Fair Value [Member] \| Mortgage backed-securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity Securities, Fair Value		0
Level 3 \| Financial Instruments Fair Value [Member] \| US States and Political Subdivisions Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity Securities, Fair Value		0
Cost \| Financial Instruments Carrying Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity Securities, Fair Value	8,430	7,331
Repurchase agreements	1,404	1,402
Short-term debt		1,150
Long-term debt	9,447	3,357
Trust preferred securities	309	309
Total liabilities	11,160	6,218
Cost \| Financial Instruments Carrying Value [Member] \| U.S. Treasury and agency
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity Securities, Fair Value	733	832
Cost \| Financial Instruments Carrying Value [Member] \| Foreign
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity Securities, Fair Value	763	916
Cost \| Financial Instruments Carrying Value [Member] \| Corporate Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity Securities, Fair Value	3,054	2,323
Cost \| Financial Instruments Carrying Value [Member] \| Mortgage backed-securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity Securities, Fair Value	1,707	1,983
Cost \| Financial Instruments Carrying Value [Member] \| US States and Political Subdivisions Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity Securities, Fair Value	2,173	1,277
Level 1 \| Financial Instruments Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity Securities, Fair Value	583	659
Short-term debt		0
Long-term debt		0
Trust preferred securities		0
Total liabilities		0
Level 1 \| Financial Instruments Fair Value [Member] \| U.S. Treasury and agency
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity Securities, Fair Value	$ 583	659
Level 1 \| Financial Instruments Fair Value [Member] \| Foreign
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity Securities, Fair Value		0
Level 1 \| Financial Instruments Fair Value [Member] \| Corporate Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity Securities, Fair Value		0
Level 1 \| Financial Instruments Fair Value [Member] \| Mortgage backed-securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity Securities, Fair Value		0
Level 1 \| Financial Instruments Fair Value [Member] \| US States and Political Subdivisions Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity Securities, Fair Value		$ 0

Total liabilities not carried at fair value.

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- Definition

Trust preferred securities not carried at fair value.

+ References

No definition available.

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- Definition

The end date of the period reflected on the cover page if a periodic report. For all other reports and registration statements containing historical data, it is the date up through which that historical data is presented. If there is no historical data in the report, use the filing date. The format of the date is CCYY-MM-DD.

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No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Fair value of investments in debt securities classified as held-to-maturity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
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- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

Amount, after the effects of master netting arrangements, of funds outstanding borrowed in the form of a security repurchase agreement between the entity and another party for the sale and repurchase of identical or substantially the same securities at a date certain for a specified price. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
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Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Repurchase Agreement Accounted for as a Collateralized Borrowing
-URI http://asc.fasb.org/extlink&oid=49203159

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- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents the amount of short-term debt existing as of the balance sheet date.

+ References

No definition available.

+ Details

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