Investment Securities (Narrative) (Details) $ in Millions	Jun. 30, 2017 USD ($) securities	Dec. 31, 2016 USD ($)
Investments [Abstract]
Pledged to secure deposits \| $	$ 1,730	$ 2,040
Investment securities in a loss position for less than twelve months	92
Investment securities in a loss position for twelve months or longer	3

Number of investment positions in available-for-sale investments that have been in a continuous unrealized loss position for greater than or equal to a year for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.

No definition available.

Name:	us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsGreaterThanOrEqualToOneYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant