Available-For-Sale And Held-To-Maturity Securities (Narrative) (Details)		3 Months Ended		6 Months Ended
		Jun. 30, 2018 USD ($) security	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) security	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Proceeds from sale of available-for-sale securities			$ 87,300,000	$ 0	$ 87,300,000
Net realized gains resulting from sale of available-for-sale securities			400,000		400,000
Unrealized gains (losses) recorded in accumulated other comprehensive loss	[1],[2],[3]	$ (11,856,000)	3,770,000	(24,927,000)	7,547,000
Financial instruments pledged as collateral		$ 2,100,000,000		$ 2,100,000,000		$ 2,200,000,000
Number of available for sale securities whose amortized costs exceeded their fair values | security		218		218
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		$ 47,636,000		$ 47,636,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses		19,451,000		19,451,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		$ 1,688,082,000		$ 1,688,082,000
Percentage of available-for-sale portfolio		48.60%		48.60%
Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security		116		116
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss		$ 47,846,000		$ 47,846,000
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss		34,182,000		34,182,000
Credit-related OTTI		0	$ 0	0	$ 0
Gross unrealized losses related to investment portfolio				95,500,000
Pledged [Member]
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Trading securities pledged		$ 2,300,000,000		$ 2,300,000,000		$ 2,000,000,000

[1] Net of tax benefit of $6.0 million and tax expense of $3.7 million for the three months ended June 30, 2018 and 2017, respectively. Net of tax benefit of $8.3 million and tax expense of $8.5 million for the six months ended June 30, 2018 and 2017, respectively.

[2] The adoption of ASU 2018-02 on January 1, 2018 resulted in a reclassification of $3.0 million to retained earnings related to cash flow hedges and investment portfolio risk. The reclassification is reflected in the activity for the six months ended June 30, 2018. See Note 2 for further details.

[3] There were no reclassifications to earnings during the three and six months ended June 30, 2018 and 2017, respectively.