Available-For-Sale Securities (Summary Of Available-For-Sale Debt Securities In A Continuous Unrealized Loss Position Deemed Not To Be Other-Than-Temporarily Impaired) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Gross Unrealized Losses	$ (30,528)	$ (4,591)
Less Than 12 Months, Estimated Fair Value	1,269,712	1,463,107
12 Months or Greater, Gross Unrealized Losses	(4,548)	(5,129)
12 Months or Greater, Estimated Fair Value	46,952	70,771
Total, Gross Unrealized Losses	(35,076)	(9,720)
Total, Estimated Fair Value	1,316,664	1,533,878
U.S. Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Gross Unrealized Losses	0	(1,020)
Less Than 12 Months, Estimated Fair Value	0	531,184
12 Months or Greater, Gross Unrealized Losses	0	0
12 Months or Greater, Estimated Fair Value	0	0
Total, Gross Unrealized Losses	0	(1,020)
Total, Estimated Fair Value	0	531,184
U.S. Government Agencies And FDIC Guaranteed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Gross Unrealized Losses	0	(463)
Less Than 12 Months, Estimated Fair Value	0	226,176
12 Months or Greater, Gross Unrealized Losses	0	0
12 Months or Greater, Estimated Fair Value	0	0
Total, Gross Unrealized Losses	0	(463)
Total, Estimated Fair Value	0	226,176
Municipal Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Gross Unrealized Losses	0	(21)
Less Than 12 Months, Estimated Fair Value	0	4,688
12 Months or Greater, Gross Unrealized Losses	0	0
12 Months or Greater, Estimated Fair Value	0	0
Total, Gross Unrealized Losses	0	(21)
Total, Estimated Fair Value	0	4,688
Non-U.S. Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Gross Unrealized Losses	(30,505)	(86)
Less Than 12 Months, Estimated Fair Value	24,741	44,317
12 Months or Greater, Gross Unrealized Losses	0	0
12 Months or Greater, Estimated Fair Value	0	0
Total, Gross Unrealized Losses	(30,505)	(86)
Total, Estimated Fair Value	24,741	44,317
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Gross Unrealized Losses	(5)	(1,749)
Less Than 12 Months, Estimated Fair Value	224,989	419,425
12 Months or Greater, Gross Unrealized Losses	0	0
12 Months or Greater, Estimated Fair Value	0	0
Total, Gross Unrealized Losses	(5)	(1,749)
Total, Estimated Fair Value	224,989	419,425
Certificates Of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Gross Unrealized Losses	(18)	(13)
Less Than 12 Months, Estimated Fair Value	1,019,982	39,987
12 Months or Greater, Gross Unrealized Losses	0	0
12 Months or Greater, Estimated Fair Value	0	0
Total, Gross Unrealized Losses	(18)	(13)
Total, Estimated Fair Value	1,019,982	39,987
Residential Mortgage And Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Gross Unrealized Losses	0	(1,239)
Less Than 12 Months, Estimated Fair Value	0	197,330
12 Months or Greater, Gross Unrealized Losses	0	0
12 Months or Greater, Estimated Fair Value	0	0
Total, Gross Unrealized Losses	0	(1,239)
Total, Estimated Fair Value	0	197,330
Student Loan-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Gross Unrealized Losses	0	0
Less Than 12 Months, Estimated Fair Value	0	0
12 Months or Greater, Gross Unrealized Losses	(4,548)	(5,129)
12 Months or Greater, Estimated Fair Value	46,952	70,771
Total, Gross Unrealized Losses	(4,548)	(5,129)
Total, Estimated Fair Value	$ 46,952	$ 70,771