Available-For-Sale And Held-To-Maturity Securities (Narrative) (Details)		3 Months Ended		9 Months Ended
		Sep. 30, 2017 USD ($) security	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) security	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Proceeds from sale of available-for-sale securities		$ 0	$ 0	$ 87,300,000	$ 0
Net realized gains resulting from sale of available-for-sale securities				400,000
Unrealized gains (losses) recorded in accumulated other comprehensive loss	[1],[2]	4,736,000	4,494,000	12,283,000	14,915,000
Financial instruments pledged as collateral		1,800,000,000		1,800,000,000		$ 2,000,000,000
Trading securities pledged		$ 2,300,000,000		$ 2,300,000,000		1,700,000,000
Number of available for sale securities whose amortized costs exceeded their fair values | security		134		134
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses				$ 13,154,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses				9,808,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		$ 856,778,000		$ 856,778,000
Percentage of available-for-sale portfolio		23.20%		23.20%
Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security		41		41
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss				$ 14,426,000
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss				8,636,000
Credit-related OTTI		$ 0	$ 0	0	$ 0
Gross unrealized losses related to investment portfolio	[3]	13,154,000		13,154,000		$ 20,411,000
Available-for-sale and Held-to-maturity Securities [Member]
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Gross unrealized losses related to investment portfolio		$ 27,600,000		$ 27,600,000

[1] Net of tax expense of $5.0 million and $5.8 million for the three months ended September 30, 2017 and 2016, respectively. Net of tax expense of $13.5 million and tax expense of $3.4 million for the nine months ended September 30, 2017 and 2016, respectively.

[2] There were no reclassifications to earnings during the three and nine months ended September 30, 2017 and 2016, respectively.

[3] Unrealized gains/(losses) related to available-for-sale securities are reported in accumulated other comprehensive loss.