Significant Accounting Policies (Policies)	6 Months Ended
Significant Accounting Policies (Policies)	Jun. 30, 2019
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Basis of Presentation	Basis of Presentation The accompanying unaudited consolidated financial statements have been prepared in accordance with the instructions to Form 10-Q and Article 10 of Regulation S-X and, accordingly, do not include all of the information and disclosures required by accounting principles generally accepted in the United States of America (“GAAP”) for annual periods. These statements should be read in conjunction with the consolidated financial statements and notes thereto included in the Annual Report on Form 10-K for the year ended December 31, 2018. The accompanying consolidated financial statements have not been audited by an independent registered public accounting firm in accordance with the standards of the Public Company Accounting Oversight Board (U.S.), but in the opinion of management such financial statements include all adjustments, consisting only of normal recurring adjustments, necessary for the fair statement of the Company’s consolidated financial position and results of operations. All material intercompany balances and transactions have been eliminated. The preparation of financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. As additional information becomes available or actual amounts become determinable, the recorded estimates are revised and reflected in operating results. The results of operations for the three and six months ended June 30, 2019 may not be indicative of the results that may be expected for the year ending December 31, 2019. The December 31, 2018 consolidated balance sheet was derived from audited financial statements, but does not include all disclosures required by GAAP for annual periods. Beginning with the second quarter of 2019, the Company changed its presentation of its insurance loss recoverable and its loss and loss adjustment expense (“LAE”) reserves related to its insured first-lien RMBS exposure. The Company’s first-lien RMBS insurance loss recoverable previously represented discounted and probability-weighted estimated recoveries, net of claims expected to be paid, when the result was a net receivable, and its first-lien RMBS loss and LAE reserves previously represented discounted and probability-weighted estimated claims, net of expected recoveries to be collected, when the result was a net payable. The Company now reports its first-lien RMBS insurance loss recoverable gross of expected claim payments and all expected claim payments are reported within loss and LAE reserves on the Company’s balance sheet. This treatment is consistent with the Company’s balance sheet presentation for insurance loss recoverable and loss and LAE reserves of its other major insured exposures. Certain amounts have been reclassified in prior years’ financial statements to conform to the current presentation. This includes a reclassification of $31 million resulting in an increase to insurance loss recoverable and a corresponding increase to loss and LAE reserves on the Company’s consolidated balance sheet as of December 31, 2018. This reclassification had no impact on total revenues, total expenses, shareholders’ equity, operating cash flows, investing cash flows, or financing cash flows for all periods presented. In addition, prior period amounts included in the Company’s disclosures have been updated to reflect the new presentation.
Recently Adopted Accounting Standards	Recently Adopted Accounting Standards Leases (Topic 842) (ASU 2016-02) In February of 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Updated (“ASU”) 2016-02, “Leases (Topic 842)”, that amends the accounting guidance for leasing transactions. ASU 2016-02 requires a lessee to classify lease contracts as finance or operating leases, and to recognize assets and liabilities for the rights and obligations created by leasing transactions with lease terms more than twelve months. ASU 2016-02 substantially retains the criteria for classifying leasing transactions as finance or operating leases. For finance leases, a lessee recognizes a right-of-use asset and a lease liability initially measured at the present value of the lease payments, and recognizes interest expense on the lease liability separately from the amortization of the right-of-use asset. For operating leases, a lessee recognizes a right-of-use asset and a lease liability initially measured at the present value of the lease payments, and recognizes lease expense on a straight-line basis. The Company adopted ASU 2016-02 in its entirety in the first quarter of 2019, using an additional (and optional) modified retrospective transition approach. Comparative periods are presented in accordance with Topic 840, Leases, and do not include any retrospective adjustments to comparative periods to reflect the adoption of ASU 2016-02. The Company recorded a right-of-use asset and lease liability of $23 million. The gross up of the assets and liabilities does not have a cumulative effect adjustment to the opening balance of retained earnings and does not impact the Company’s statement of operations. Refer to “Note 14: Commitments and Contingencies” for information about the Company’s lease commitments. Disclosure Update and Simplification In August of 2018, the Securities and Exchange Commission (“SEC”) published Release No. 33-10532, Disclosure Update and Simplification, which amends certain disclosure requirements that were redundant, duplicative, overlapping, outdated or superseded. In addition, these amendments updated the disclosure requirements for the interim financial statement requirements to include a reconciliation of each caption of shareholders’ equity, in the notes or as a separate statement for each period for which a statement of comprehensive income is required to be included. The Company updated the presentation of its consolidated statements of changes in shareholders’ equity for all periods presented beginning in the first quarter of 2019. The Company has not adopted any other new accounting pronouncements that had a material impact on its consolidated financial statements.