Regulatory Matters - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Sep. 30, 2017	Dec. 31, 2005	Jun. 30, 2003	Dec. 31, 2017	Dec. 31, 2016
Regulatory Capital Requirements [Abstract]
Proceeds from (repurchase of) trust preferred securities	$ (8)	$ 18	$ 18	$ 10	$ 18
Tier 1 common equity, adequately capitalized ratio, conservation buffer				2.50%

The cash inflow from issuance of trust preferred securities, net of the cash outflow for repurchasing trust preferred securities, by a business trust or other special purpose entity, mainly established by a bank holding entity, to third party investors. The trust's assets are deeply subordinated debentures of the bank holding entity. Most trust preferred securities are subject to a mandatory redemption upon the repayment of the debentures.

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration