Available-For-Sale And Held-To-Maturity Securities (Narrative) (Details)		3 Months Ended
		Mar. 31, 2018 USD ($) security	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
Investments Debt And Equity Securities [Abstract]
Proceeds from sale of available-for-sale securities		$ 0	$ 0
Unrealized gains (losses) recorded in accumulated other comprehensive loss	[1],[2],[3]	(13,071,000)	3,777,000
Financial instruments pledged as collateral		2,100,000,000		$ 2,200,000,000
Trading securities pledged		$ 2,100,000,000		$ 2,000,000,000
Number of available for sale securities whose amortized costs exceeded their fair values | security		226
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		$ 38,541,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses		17,931,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		$ 1,564,910,000
Percentage of available-for-sale portfolio		42.10%
Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security		62
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss		$ 33,904,000
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss		30,505,000
Credit-related OTTI		0	$ 0
Gross unrealized losses related to investment portfolio		$ 72,400,000

[1] Net of tax benefit of $2.3 million and tax expense of $4.8 million for the three months ended March 31, 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 credit risk. See Note 2 for further details.

[3] There were no reclassifications to earnings during the three months ended March 31, 2018 and 2017, respectively.