Investment Securities (Narrative) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2022 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2021 USD ($)
Debt Securities, Available-for-sale [Line Items]
Percentage decrease requiring a review for impairment	20.00%
Fair value of securities on impairment watch list	$ 13,100		$ 13,400
Debt Securities, Available-for-sale, Unrealized Loss Position	12,228,766		9,047,662
Unrealized Loss on AFS Debt Securities	690,051		132,929
AFS securities in loss position at period-end, change in unrealized loss	557,100
Securities pledged as collateral	5,200,000		6,400,000
Securities pledged as collateral and may be sold or re-pledged	$ 201,000
Number of investments in a single issuer that exceed 10% of stockholder's equity	0
No investment in a single issuer exceeds this percentage of stockholder's equity	10.00%
U.S. government and federal agency obligations
Debt Securities, Available-for-sale [Line Items]
U.S. Treasury inflation-protected securities held, at fair value	$ 399,400
Debt Securities, Available-for-sale, Unrealized Loss Position	390,451		296,492
Unrealized Loss on AFS Debt Securities	13,082		$ 2,241
Equity Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Equity Securities, FV-NI, Unrealized Gain (Loss)	(287)	$ (35)
Other Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Fair value other securities adjustments, net	$ 7,450	$ 8,365