Derivative Financial Instruments - Notional Amount of Interest Rate Swap Agreements Designated as Fair Value and Cash Flow Hedges (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
Jun. 30, 2017	Dec. 31, 2016
Derivative [Line Items]
Total	$ 10,157
Investment securities available-for-sale
Derivative [Line Items]
Investment securities available-for-sale	1,364
Long-term debt
Derivative [Line Items]
Long-term debt	8,493
Floating-rate loans
Derivative [Line Items]
Long-term debt	300
Fair Value Hedges
Derivative [Line Items]
Total	9,857	$ 10,169
Increase in carrying value of long-term debt	12	(15)
Fair Value Hedges \| Investment securities available-for-sale
Derivative [Line Items]
Investment securities available-for-sale	1,364	1,444
Fair Value Hedges \| Long-term debt
Derivative [Line Items]
Long-term debt	8,493	$ 8,725
Fair Value Hedges \| Floating-rate loans
Derivative [Line Items]
Long-term debt	0
Cash Flow Hedges
Derivative [Line Items]
Total	300
Cash Flow Hedges \| Investment securities available-for-sale
Derivative [Line Items]
Investment securities available-for-sale	0
Cash Flow Hedges \| Long-term debt
Derivative [Line Items]
Long-term debt	0
Cash Flow Hedges \| Floating-rate loans
Derivative [Line Items]
Long-term debt	$ 300

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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- Definition

Increase (Decrease) In Carrying Value Of Long Term Debt

+ References

No definition available.

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- Definition

Nominal or face amount used to calculate payments on the derivative asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5579245-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Notional Amount
-URI http://asc.fasb.org/extlink&oid=6519104

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5580258-113959

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- Definition

Nominal or face amount used to calculate payments on the derivative liability.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Notional Amount
-URI http://asc.fasb.org/extlink&oid=6519104

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5579245-113959

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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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