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Fair Value Measurements (Summary of Quantitative Information About Level 3 Fair Value Measurements) (Details) | 12 Months Ended
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Dec. 31, 2020
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fair Value, Discounted Cash Flow, Valuation Techniques | Discounted cash flow |
Auction Rate Securities [Member] |  |
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fair Value, Discounted Cash Flow, Valuation Techniques | Discounted cash flow |
Fair Value, Estimated Market Recovery Period, Years | 5 years |
Auction Rate Securities [Member] | Minimum [Member] |  |
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fair Value, Estimated Market Rate, Percent | 1.50% |
Auction Rate Securities [Member] | Maximum [Member] |  |
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fair Value, Estimated Market Rate, Percent | 1.70% |
Auction Rate Securities [Member] | Weighted Average [Member] |  |
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fair Value, Estimated Market Recovery Period, Years | 5 years | [1]
Fair Value, Estimated Market Rate, Percent | 1.50% | [1]
Private Equity Funds [Member] |  |
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fair Value, Market Comparable Companies, Valuation Techniques | Market comparable companies |
Private Equity Funds [Member] | Minimum [Member] |  |
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fair Value Inputs, Earnings before Interest, Taxes, Depreciation, and Amortization Multiple | 4.0 |
Private Equity Funds [Member] | Maximum [Member] |  |
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fair Value Inputs, Earnings before Interest, Taxes, Depreciation, and Amortization Multiple | 6.0 |
Private Equity Funds [Member] | Weighted Average [Member] |  |
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fair Value Inputs, Earnings before Interest, Taxes, Depreciation, and Amortization Multiple | 5.4 | [1]
Mortgage Loan Commitments [Member] |  |
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fair Value, Discounted Cash Flow, Valuation Techniques | Discounted cash flow |
Mortgage Loan Commitments [Member] | Minimum [Member] |  |
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Probability of Funding | 56.70% |
Embedded Servicing Value, Mortgage Loan Commitments, Discounted Cash Flow | 0.50% |
Mortgage Loan Commitments [Member] | Maximum [Member] |  |
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Probability of Funding | 98.80% |
Embedded Servicing Value, Mortgage Loan Commitments, Discounted Cash Flow | 1.00% |
Mortgage Loan Commitments [Member] | Weighted Average [Member] |  |
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Probability of Funding | 85.70% | [1]
Embedded Servicing Value, Mortgage Loan Commitments, Discounted Cash Flow | 0.90% | [1]
[1] | * Unobservable inputs were weighted by the relative fair value of the instruments.

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