Financial Instruments Subject to Off-Balance Sheet Credit Risk (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Securities Financing Transaction, Fair Value [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fair value of securities borrowed	$ 215	$ 213

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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Period Type:	duration