Fair Value Measurements (Summary Of Quantitative Information About Level 3 Fair Value Measurements) (Details)	9 Months Ended
	Sep. 30, 2017 Rate
Auction Rate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Valuation Technique, Discounted cash flow	Discounted cash flow
Unobservable Input, Estimated market recovery period	5 years
Auction Rate Securities [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Unobservable Input, Estimated market rate	2.80%
Auction Rate Securities [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Unobservable Input, Estimated market rate	3.10%
Private Equity Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Valuation Technique, Market comparable companies	Market comparable companies
Private Equity Investments [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Inputs, Earnings before Interest, Taxes, Depreciation, and Amortization Multiple	4.0
Private Equity Investments [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Inputs, Earnings before Interest, Taxes, Depreciation, and Amortization Multiple	5.8
Mortgage Loan Commitments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Valuation Technique, Discounted cash flow	Discounted cash flow
Weighted Average, Probability of Funding	79.10%
Weighted Average, Embedded Servicing Value	1.10%
Mortgage Loan Commitments [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Probability of Funding	50.90%
Embedded Servicing Value	(0.30%)
Mortgage Loan Commitments [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Probability of Funding	100.00%
Embedded Servicing Value	2.20%