Contingencies And Other Disclosures (Narrative I) (Details) shares in Millions	3 Months Ended		36 Months Ended	48 Months Ended
	Mar. 31, 2018 USD ($) entity shares	Jun. 30, 2015 USD ($)	Dec. 31, 2007 USD ($)	Dec. 31, 2008 USD ($)	Dec. 31, 2017 USD ($)	Mar. 31, 2008 shares
Loss Contingencies [Line Items]
Estimated litigation liability	$ 42,600,000
Number of GSEs to which conventional conforming single-family mortgage loans were predominately sold to | entity	2
Loan-to-value ratio at origination	80.00%
Mortgage loans originated and sold to agencies				$ 69,500,000,000
Loans sold to GSEs				57,600,000,000
Loans guaranteed by Ginnie Mae				$ 11,900,000,000
Loans included in FH proprietary securitizations			$ 26,700,000,000
Accrued losses on loan repurchase exposure	$ 34,200,000				$ 34,200,000
Fha Insured
Loss Contingencies [Line Items]
Litigation settlement, expense		$ 212,500,000
Amount of Insurance recoveries company is pursuing		$ 75,000,000
Mortgage Securitization Litigation
Loss Contingencies [Line Items]
Investment in proprietary securitizations subject to lawsuits	83,400,000
Investment in proprietary securitizations subject to indemnifications	$ 409,900,000
Visa Class B Shares
Loss Contingencies [Line Items]
Number of Visa Class B shares | shares	1.0					2.4
Derivative liability	$ 5,600,000				$ 5,600,000
Historical cost	$ 0
Estimated conversion ratio	165.00%
Contingent liability	$ 800,000
Value of holdings of Visa Class B Shares if converted into Class A shares at the current conversion ratio	206,000,000
Subservicer expenditure reimbursement amount disputed
Loss Contingencies [Line Items]
Actual damages sought by plaintiff	43,500,000
Minimum
Loss Contingencies [Line Items]
Estimated reasonably possible losses in excess of currently established liabilities	0
Maximum
Loss Contingencies [Line Items]
Estimated reasonably possible losses in excess of currently established liabilities	$ 22,000,000