Summary of Significant Accounting Principles - Collateral (Details) - USD ($) $ in Billions |
12 Months Ended | |
|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
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| Accounting Policies [Abstract] | ||
| Securities held as collateral, fair value | $ 561.9 | $ 452.1 |
| Securities received as collateral, amount re-pledged and sold | $ 476.1 | $ 372.0 |
| X | ||||||||||
- References No definition available.
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| X | ||||||||||
- Definition The carrying amount (fair value) as of the balance sheet date of securities held that had been pledged by counterparties under financing and lending arrangements, pursuant to which the entity has the right by agreement or custom to sell or re-pledge such securities. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
- Definition The fair value of collateral received that has been sold or re-pledged and is owed to the debtor (transferor) upon settlement of the related contractual obligation under which it was received. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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