Derivative Financial Instruments - Amounts Related to Cash Flow Hedges (Details) - Cash Flow Hedges - Interest Rate Contracts - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Pre-tax gain (loss) recognized in OCI	$ 93	$ 4
Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Amounts reclassified from AOCI into interest expense	(11)	8
Deposits
Derivative Instruments, Gain (Loss) [Line Items]
Pre-tax gain (loss) recognized in OCI	21	0
Deposits \| Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Amounts reclassified from AOCI into interest expense	(2)	0
Long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Pre-tax gain (loss) recognized in OCI	72	0
Long-term debt \| Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Amounts reclassified from AOCI into interest expense	$ (9)	$ 0

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.

No definition available.

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- Definition

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=84234895&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=84234895&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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