Short-Term Borrowings - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Short-term Debt [Line Items]
Money Pledged as Collateral for FHLB Advance Borrowings	$ 25	$ 25
FHLB Advances
Short-term Debt [Line Items]
Commercial real estate and residential mortgage loans pledged under blanket agreement	$ 1,789	$ 1,909

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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