Derivative Financial Instruments - Narrative (Details) $ in Millions	12 Months Ended
Dec. 31, 2015 USD ($) security	Dec. 31, 2014 USD ($)
Derivative [Line Items]
Cash collateral received for derivative instruments	$ 1,400	$ 1,790
Cash collateral provided for derivative instruments	1,650	4,790
Fair value of derivative liabilities	11,153	15,234
Fair value of collateral posted	$ 32	$ 105
Securities weighted average life	5 years 4 months 10 days	5 years 10 months 18 days
Credit swap agreements
Derivative [Line Items]
Fair value of derivative liabilities	$ 1,050	$ 2,540
Maximum additional amount of payments related to termination events	$ 1,020	$ 2,430
Interest rate swap \| Fair Value Hedges \| 5.38% senior note due 2017
Derivative [Line Items]
Fixed interest rate	5.38%
Interest rate swap \| Fair Value Hedges \| 1.35% senior note due 2018
Derivative [Line Items]
Fixed interest rate	1.35%
Interest rate swap \| Fair Value Hedges \| 2.55% notes due 2020
Derivative [Line Items]
Fixed interest rate	2.55%
Interest rate swap \| Fair Value Hedges \| 4.38% note due 2021
Derivative [Line Items]
Fixed interest rate	4.38%
Interest rate swap \| Fair Value Hedges \| 3.70% notes due in 2023
Derivative [Line Items]
Fixed interest rate	3.70%
Interest rate swap \| Fair Value Hedges \| 3.30% notes due 2024
Derivative [Line Items]
Fixed interest rate	3.30%
Interest rate swap \| Fair Value Hedges \| 3.55% notes due 2025
Derivative [Line Items]
Fixed interest rate	3.55%
Interest rate swap \| Fair Value Hedges \| 4.96% subordinated note due 2018
Derivative [Line Items]
Fixed interest rate	4.956%
Interest rate swap \| Fair Value Hedges \| 3.10% subordinated note due 2023
Derivative [Line Items]
Fixed interest rate	3.10%
Interest rate swap \| Fair Value Hedges \| Senior notes
Derivative [Line Items]
Number of securities \| security	7
Interest rate swap \| Fair Value Hedges \| Subordinated note
Derivative [Line Items]
Number of securities \| security	2

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Cash Collateral Received For Derivative Instruments

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Securities Weighted Average Life, Years

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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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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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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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Fixed interest rate related to the interest rate derivative.

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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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