Derivative Financial Instruments - Narrative (Details)	3 Months Ended	12 Months Ended
Mar. 31, 2018 USD ($) security	Dec. 31, 2017 USD ($)
Derivative [Line Items]
Cash collateral received for derivative instruments	$ 1,450,000,000	$ 2,550,000,000
Cash collateral provided for derivative instruments	2,070,000,000	869,000,000
Fair value of derivative liabilities	$ 11,557,000,000	$ 11,852,000,000
Weighted average life of trusts	3 years 10 months 24 days	4 years 7 months
LIBOR Indexed Floating Rate Loans
Derivative [Line Items]
Term of debt instrument	4 years 2 months 12 days
Credit swap agreements
Derivative [Line Items]
Fair value of derivative liabilities	$ 1,570,000,000
Fair value of collateral posted	28,000,000
Maximum additional amount of payments related to termination events	$ 1,540,000,000
Interest rate swap \| Fair Value Hedges \| Senior notes
Derivative [Line Items]
Number of securities \| security	8
Interest rate swap \| Fair Value Hedges \| Subordinated note
Derivative [Line Items]
Number of securities \| security	1

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Cash Collateral Received For Derivative Instruments

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Weighted Average Life Of Trusts

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- Definition

The aggregate fair value of additional assets that would be required to be posted as collateral for derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

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Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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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.

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The number of derivative instruments of a particular group held by the entity.

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