Financial Derivatives (Gains (Losses) on Derivatives and Related Cash Flows - Cash Flow Hedges) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Net unrealized gains (losses) on cash flow hedge derivatives	$ (47)	$ (125)	$ (134)	$ 138
Cash Flow Hedging [Member] \| Interest Rate Contracts [Member] \| Designated as Hedging Instruments under GAAP [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) on derivatives recognized in OCI – (effective portion)	(2)	(63)	15	328
Less: Gains (losses) reclassified from accumulated OCI into income – (effective portion)	45	62	149	190
Net unrealized gains (losses) on cash flow hedge derivatives	(47)	(125)	(134)	138
Cash Flow Hedging [Member] \| Interest Rate Contracts [Member] \| Interest Income [Member] \| Designated as Hedging Instruments under GAAP [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Less: Gains (losses) reclassified from accumulated OCI into income – (effective portion)	43	61	144	190
Cash Flow Hedging [Member] \| Interest Rate Contracts [Member] \| Noninterest Income [Member] \| Designated as Hedging Instruments under GAAP [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Less: Gains (losses) reclassified from accumulated OCI into income – (effective portion)	$ 2	$ 1	$ 5

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The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5624171-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4D
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5624177-113959

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- Definition

The effective portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments that was recognized in other comprehensive income during the current period.

+ References

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- Definition

Amount before tax, after reclassification adjustments, of increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=66004124&loc=SL7669646-108580

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