Aspen Insurance Holdings Limited (AHL-PC) 10-Q 8 May 19 2019 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information	3 Months Ended
	Mar. 31, 2019shares
Document and Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Trading Symbol	AHL
Entity Registrant Name	ASPEN INSURANCE HOLDINGS LTD
Entity Central Index Key	0001267395
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Common Stock, Shares Outstanding	60,395,839

UNAUDITED CONDENSED CONSOLIDATE

UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Investments:
Fixed income securities, available for sale at fair value (amortized cost — $5,016.5 and $5,282.3)	$ 5,040.5	$ 5,230.7
Fixed income securities, trading at fair value (amortized cost — $1,273.1 and $1,205.0)	1,289.3	1,187.8
Short-term investments, available for sale at fair value (amortized cost — $160.7 and $105.6)	160.9	105.6
Short-term investments, trading at fair value (amortized cost — $ 81.0 and $9.5)	81	9.5
Catastrophe bonds, trading at fair value (cost — $39.5 and $37.9)	38.1	36.2
Investments, equity method	67	67.1
Other investments	104	102.5
Total investments	6,780.8	6,739.4
Cash and cash equivalents (including $21.2 and $26.9 within consolidated variable interest entities)	975.9	1,083.7
Reinsurance recoverables
Unpaid losses	2,122.9	2,077.6
Ceded unearned premiums	647.5	558.8
Receivables
Underwriting premiums	1,686.6	1,459.3
Other	139.9	121.2
Funds withheld	92	91.8
Deferred policy acquisition costs	288.4	248.5
Derivatives at fair value	10.8	14.6
Receivables for securities sold	6.4	3.2
Office properties and equipment	72.5	73.1
Right-of-use operating lease assets	91.4	0
Deferred tax assets	35.6	35.4
Other assets	1.5	0
Intangible assets and goodwill	25.9	26.3
Total assets	12,978.1	12,532.9
Insurance reserves
Losses and loss adjustment expenses	7,000.3	7,074.2
Unearned premiums	1,917.6	1,709.1
Total insurance reserves	8,917.9	8,783.3
Payables
Reinsurance premiums	544.2	405.6
Current taxation	5	0.1
Accrued expenses and other payables	218.5	248.1
Operating lease liabilities	93.9	0
Liabilities under derivative contracts	56.7	15.1
Total payables	918.3	668.9
Long-term debt	424.7	424.7
Total liabilities	10,260.9	9,876.9
Commitments and contingent liabilities (see Note 17)	0	0
SHAREHOLDERS’ EQUITY
Ordinary shares, value	0.6	0.1
Preference shares:
Non-controlling interest	3.5	3.7
Additional paid-in capital	967.8	967.5
Retained earnings	1,807.4	1,806.6
Accumulated other comprehensive income, net of taxes	(62.1)	(121.9)
Total shareholders’ equity	2,717.2	2,656
Total liabilities and shareholders’ equity	12,978.1	12,532.9
5.95% preference shares
Preference shares:
Preference shares, value	0	0
5.625% preference shares
Preference shares:
Preference shares, value	$ 0	$ 0

UNAUDITED CONDENSED CONSOLIDA_2

UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019		Dec. 31, 2018
Fixed income securities, available for sale, amortized cost	$ 5,016.5		$ 5,282.3
Fixed income securities, trading at fair value, amortized cost	1,273.1		1,205
Equity securities, trading at fair value, cost	0		0
Catastrophe bonds, trading at fair value, cost	39.5		37.9
Cash and cash equivalents, within consolidated VIEs	$ 21.2		$ 26.9
Ordinary shares, par value (in usd per share)	$ 0.01	[1]	$ 0.0015144558
Ordinary shares, issued (in shares)	60,395,839		59,743,156
Common stock issued (in shares)			59,474,085
Preference shares, par value (in usd per share)	$ 0.0015144558		$ 0.0015144558
5.95% preference shares
Preference shares, issued (in shares)	11,000,000		11,000,000
Preference shares, rate	5.95%		5.95%
Preference shares, par value (in usd per share)	$ 0.0015144558		$ 0.0015144558
5.625% preference shares
Preference shares, issued (in shares)	10,000,000		10,000,000
Preference shares, rate	5.625%		5.625%
Preference shares, par value (in usd per share)	$ 0.0015144558		$ 0.0015144558
Short-term Investments
Short term investments, available for sale at fair value	$ 160.7		$ 105.6
Short term investments, trading at fair value
Short term investments, trading at fair value	$ 81		$ 9.5
[1]	On February 15, 2019, the Company completed its previously announced merger (the “Merger”) with Highlands Merger Sub, Ltd. (“Merger Sub”), a wholly owned subsidiary of Highlands Holdings, Ltd. (“Parent”). As a result of the Merger, a change in control of the Company occurred and the Company is now a wholly owned subsidiary of Parent. At the effective time of the Merger, each of the Company’s issued and outstanding ordinary shares (other than ordinary shares owned by the Company as treasury shares, owned by any subsidiary of the Company or owned by Parent, Merger Sub or any subsidiary thereof) was automatically canceled and converted into the right to receive $42.75 in cash, without interest and less any required tax withholdings. The ordinary shares of the Company ceased trading on the New York Stock Exchange prior to the opening of trading on February 15, 2019. Therefore, earnings per share data is no longer considered meaningful for both the current reporting period and for the comparative period and has been excluded. For more information on the Merger, refer to Note 1 of these unaudited condensed consolidated financial statements.

UNAUDITED CONDENSED CONSOLIDA_3

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND OTHER COMPREHENSIVE INCOME - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Revenues
Net earned premium		$ 510.6	$ 533.5
Net investment income		51.5	47.3
Realized and unrealized investment gains		42	100.6
Other income		1.7	2.1
Total revenues		605.8	683.5
Expenses
Losses and loss adjustment expenses		311.8	310.2
Amortization of deferred policy acquisition costs		88.2	90.8
General, administrative and corporate expenses		137.3	121
Interest on long-term debt		5.5	7.4
Change in fair value of derivatives		53.3	(23.5)
Change in fair value of loan notes issued by variable interest entities		1.5	(1)
Realized and unrealized investment losses		6.2	138.3
Net realized and unrealized foreign exchange (gains)/losses		(5.1)	4.7
Other expenses		0.9	1.2
Total expenses		599.6	649.1
Income from operations before income tax		6.2	34.4
Income tax benefit/(expense)		4.4	(3.6)
Net income		10.6	30.8
Amount attributable to non-controlling interest		0.2	(0.2)
Net income attributable to Aspen Insurance Holdings Limited’s ordinary shareholders		10.8	30.6
Available for sale investments:
Reclassification adjustment for net realized gains on investments included in net income		0.2	(0.1)
Change in net unrealized gains/(losses) on available for sale securities held		75.4	(82.8)
Net change from current period hedged transactions		1.7	0.9
Change in foreign currency translation adjustment		(14.7)	(8.1)
Other comprehensive income/(loss), gross of tax		62.6	(90.1)
Tax thereon:
Reclassification adjustment for net realized gains on investments included in net income		0	0.1
Change in net unrealized gains/(losses) on available for sale securities held		(5.2)	5.4
Net change from current period hedged transactions		(0.1)	(0.2)
Change in foreign currency translation adjustment		2.5	1.6
Total tax on other comprehensive income		(2.8)	6.9
Other comprehensive income/(loss), net of tax		59.8	(83.2)
Total comprehensive income/(loss) attributable to Aspen Insurance Holdings Limited’s ordinary shareholders		$ 70.6	$ (52.6)
Ordinary shares, issued (in shares)		60,395,839
Ordinary shares, par value (in usd per share)	[1]	$ 0.01
[1]	On February 15, 2019, the Company completed its previously announced merger (the “Merger”) with Highlands Merger Sub, Ltd. (“Merger Sub”), a wholly owned subsidiary of Highlands Holdings, Ltd. (“Parent”). As a result of the Merger, a change in control of the Company occurred and the Company is now a wholly owned subsidiary of Parent. At the effective time of the Merger, each of the Company’s issued and outstanding ordinary shares (other than ordinary shares owned by the Company as treasury shares, owned by any subsidiary of the Company or owned by Parent, Merger Sub or any subsidiary thereof) was automatically canceled and converted into the right to receive $42.75 in cash, without interest and less any required tax withholdings. The ordinary shares of the Company ceased trading on the New York Stock Exchange prior to the opening of trading on February 15, 2019. Therefore, earnings per share data is no longer considered meaningful for both the current reporting period and for the comparative period and has been excluded. For more information on the Merger, refer to Note 1 of these unaudited condensed consolidated financial statements.

UNAUDITED CONDENSED CONSOLIDA_4

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY - USD ($) $ in Millions		Total	Ordinary shares	Preference shares	Non-controlling interest	Additional paid-in capital	Additional paid-in capitalOrdinary shares	Retained earnings	Retained earningsOrdinary shares	Retained earningsPreference shares	Cumulative foreign currency translation adjustments, net of taxes:	Loss on derivatives, net of taxes:	Unrealized appreciation on investments, net of taxes:
Shareholder's equity, beginning balance at Dec. 31, 2017			$ 0.1	$ 0	$ 2.7	$ 954.7		$ 2,026.9			$ (67.7)	$ 2.1	$ 9.7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net change attributable to non-controlling interest for the period		$ (0.2)			0.2			(0.2)
Ordinary shares canceled, shares			0
New ordinary shares issued			0				$ 0.2
Share-based compensation						4.6
Net income for the period		30.8						30.8
Dividends on ordinary shares									$ (14.3)
Dividends on preference shares										$ (7.6)
Change for the period, net of income tax											(6.5)		(77.4)
Shareholder's equity, ending balance at Mar. 31, 2018		2,859	0.1	0	2.9	959.5		2,035.6			(74.2)	2.8	(67.7)
Shareholder's equity, beginning balance at Dec. 31, 2017			0.1	0	2.7	954.7		2,026.9			(67.7)	2.1	9.7
Shareholder's equity, ending balance at Dec. 31, 2018		2,656	0.1	0	3.7	967.5		1,806.6			(55.4)	0.3	(66.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net change from current period hedged transactions												0.7
Total accumulated other comprehensive (loss), net of taxes		(139.1)
Cumulative effect of new accounting principle in period of adoption | Accounting Standards Update 2016-09	[1]							0
Total accumulated other comprehensive (loss), net of taxes		(121.9)
Net change attributable to non-controlling interest for the period		0.2			(0.2)			0.2
Ordinary shares canceled, shares			(0.1)
New ordinary shares issued			0.6				$ 0.3
Share-based compensation						0
Net income for the period		10.6						10.6
Dividends on ordinary shares									$ 0
Dividends on preference shares										$ (7.6)
Change for the period, net of income tax											(12.2)		70.4
Shareholder's equity, ending balance at Mar. 31, 2019		2,717.2	$ 0.6	$ 0	$ 3.5	$ 967.8		1,807.4			$ (67.6)	1.9	$ 3.6
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net change from current period hedged transactions												$ 1.6
Total accumulated other comprehensive (loss), net of taxes		$ (62.1)
Cumulative effect of new accounting principle in period of adoption | Accounting Standards Update 2016-09	[1]							$ (2.4)
[1]	The $2.4 million relates to the cumulative effect-adjustment to opening retained earnings as a result of the recognition of operating lease right-of-use assets and corresponding liabilities on the balance sheet following the adoption of ASU 2016-02. The adjustment has been applied using a modified retrospective approach.

UNAUDITED CONDENSED CONSOLIDA_5

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows (used in) operating activities:
Net income	$ 10.6	$ 30.8
Proportion due to non-controlling interest	0.2	(0.2)
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	8.9	10.6
Share-based compensation	0	4.6
Realized and unrealized investment gains	(42)	(100.6)
Realized and unrealized investment losses	6.2	138.3
Deferred taxes	(0.2)	0.6
Change in fair value of loan notes issued by variable interest entities	1.5	(1)
Net realized and unrealized investment foreign exchange losses/(gains)	38.7	(1.7)
Net change from current period hedged transactions	1.6	0.7
Amortization of right-of-use operating lease assets	3.3	0
Interest on operating lease liabilities	1.2	0
Insurance reserves:
Losses and loss adjustment expenses	(132)	(91.8)
Unearned premiums	203.4	274.9
Reinsurance recoverables:
Unpaid losses	(43.9)	(90.4)
Ceded unearned premiums	(88.1)	(167.7)
Other receivables	(19.1)	42.8
Deferred policy acquisition costs	(39.3)	(25.5)
Reinsurance premiums payable	139.2	130.5
Funds withheld	(0.2)	(3.1)
Premiums receivable	(236.4)	(240.7)
Income tax payable	5.5	(3.6)
Accrued expenses and other payables	(38)	(10.4)
Fair value of derivatives and settlement of liabilities under derivatives	45.4	(7.9)
Long-term debt and loan notes issued by variable interest entities	0	(12)
Operating lease liabilities	(4.5)	0
Other assets	(1.5)	0
Net cash (used in) operating activities	(179.5)	(122.8)
Cash flows from investing activities:
(Purchases) of fixed income securities — Available for sale	(263.6)	(647.9)
(Purchases) of fixed income securities — Trading	(212)	(532.9)
Proceeds from sales and maturities of fixed income securities — Available for sale	538.9	388.5
Proceeds from sales and maturities of fixed income securities — Trading	218.3	507.4
(Purchases) of equity securities — Trading	0	(16.5)
Net (purchases) of catastrophe bonds — Trading	(1.5)	(1.5)
Proceeds from sales of equity securities — Trading	0	505.6
(Purchases) of short-term investments — Available for sale	(90.4)	(8.6)
Proceeds from sales of short-term investments — Available for sale	21.2	44
(Purchases) of short-term investments — Trading	(143)	(6)
Proceeds from sales of short-term investments — Trading	14.2	51.4
Net change in (payable)/receivable for securities sold	1.4	109.8
Net (purchases) of other investments	0	0
Net (purchases) of equipment	(3.6)	(8)
Net cash from investing activities	79.9	385.3
Cash flows (used in) financing activities:
Proceeds from the issuance of ordinary shares, net of issuance costs	0.9	0.2
Ordinary shares canceled	(0.1)	0
Repayment of long-term debt issued by Silverton	(0.2)	(45.8)
Dividends paid on ordinary shares	0	(14.3)
Dividends paid on preference shares	(7.6)	(7.6)
Cash paid for tax withholding purposes	(2.8)	(4.2)
Net cash (used in) financing activities	(9.8)	(71.7)
Effect of exchange rate movements on cash and cash equivalents	1.6	1.3
(Decrease)/increase in cash and cash equivalents	(107.8)	192.1
Cash and cash equivalents at beginning of period	1,083.7	1,054.8
Cash and cash equivalents at end of period	975.9	1,246.9
Supplemental disclosure of cash flow information:
Net cash (received) during the period for income tax	(2.3)	(0.8)
Cash paid during the period for interest	$ 5.5	$ 7.4

History, Organization and Busin

History, Organization and Business Combination	3 Months Ended
	Mar. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
History and Organization and Business Combination	History, Organization and Business Combination History and Organization. Aspen Insurance Holdings Limited (“Aspen Holdings”) was incorporated on May 23, 2002 as a holding company headquartered in Bermuda. We underwrite specialty insurance and reinsurance on a global basis through our Operating Subsidiaries (as defined below) based in Bermuda, the United States and the United Kingdom: Aspen Insurance UK Limited (“Aspen U.K.”) and Aspen Underwriting Limited (corporate member of Lloyd’s Syndicate 4711, “AUL” and managed by Aspen Managing Agency Limited (“AMAL”)) (United Kingdom), Aspen Bermuda Limited (“Aspen Bermuda”) (Bermuda), Aspen Specialty Insurance Company (“Aspen Specialty”) and Aspen American Insurance Company (“AAIC”) (United States) (collectively, the “Operating Subsidiaries”). We also have branches in Australia, Canada, Ireland, Singapore, Switzerland and the United Arab Emirates. We established Aspen Capital Management, Ltd. and other related entities (collectively, “ACM”) to leverage our existing underwriting franchise, increase our operational flexibility in the capital markets and provide investors direct access to our underwriting expertise. References to the “Company,” the “Group,” “we,” “us” or “our” refer to Aspen Holdings or Aspen Holdings and its subsidiaries. Business Combination. On February 15, 2019, the Company completed its previously announced merger with Highlands Merger Sub, Ltd. (“Merger Sub”), a wholly owned subsidiary of Highlands Holdings, Ltd. (“Parent”). Pursuant to the Agreement and Plan of Merger, dated as of August 27, 2018, by and among the Company, Parent and Merger Sub (the “Merger Agreement”), and the statutory merger agreement required in accordance with Section 105 of the Bermuda Companies Act 1981, as amended (the “Companies Act”), by and among the Company, Parent and Merger Sub, dated as of February 15, 2019, Merger Sub merged with and into the Company in accordance with the Companies Act (the “Merger”), with the Company continuing as the surviving company and as a wholly owned subsidiary of Parent. Parent, a Bermuda exempted company, is an affiliate of certain investments funds managed by affiliates of Apollo Global Management, LLC, a leading global investment manager (collectively with its subsidiaries, “Apollo”). Pursuant to the Merger Agreement, at the effective time of the Merger, each issued and outstanding ordinary share of the Company (other than ordinary shares owned by the Company as treasury shares, owned by any subsidiary of the Company or owned by Parent, Merger Sub or any subsidiary thereof) was automatically canceled and converted into the right to receive $42.75 in cash, without interest and less any required tax withholdings. Pursuant to the terms of the Merger Agreement, the memorandum of association and bye-laws of Merger Sub immediately prior to the effective time of the Merger became the memorandum of association and bye-laws, respectively, of the Company at the effective time of the Merger and will remain the memorandum of association (the “Altered Memorandum of Association”) and bye-laws, respectively, of the Company, until changed or amended as provided therein or pursuant to applicable law. The Company’s authorized share capital, as set out in the Altered Memorandum of Association, is $745,434 divided into 70,000,000 ordinary shares of par value $0.01 and 30,000,000 preference shares of par value 0.15144558¢ . Immediately prior to the effective time of the Merger, Parent held 60,395,839 of ordinary shares of Merger Sub, par value $0.01 . Pursuant to the terms of the Merger Agreement, each common share of Merger Sub issued and outstanding immediately prior to the effective time of the Merger was canceled and converted into and became one duly authorized, validly issued, fully paid and non-assessable ordinary share, par value of $0.01 , of the Company, as the surviving company. In connection with the consummation of the Merger, the Company’s ordinary shares ceased trading on the New York Stock Exchange (the “NYSE”) prior to the opening of trading on February 15, 2019. Each of the Company’s issued and outstanding 5.95% Fixed-to-Floating Rate Perpetual Non-Cumulative Preference Shares and 5.625% Perpetual Non-Cumulative Preference Shares (collectively, the “Preference Shares”) remained issued and outstanding following the Merger, listed on the NYSE and entitled to the same dividend and all other preferences, privileges, rights, qualifications, limitations and restrictions set forth in the applicable certificate of designation. For information on the treatment of the Company’s outstanding equity awards in connection with the Merger, refer to Note 14 of the unaudited condensed consolidated financial statements in this report. Additional information about the Merger is set forth in the Company’s Current Report on Form 8-K filed with the United States Securities and Exchange Commission (the “SEC”) on February 15, 2019 and the exhibits thereto, and on August 28, 2018 and the exhibits thereto, including the Merger Agreement, and the Company’s definitive proxy statement on Schedule 14A filed with the SEC on November 6, 2018.

Basis of Preparation

Basis of Preparation	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Preparation The accompanying unaudited condensed consolidated financial statements have been prepared on the basis of generally accepted accounting principles in the United States (“U.S. GAAP”) for interim financial information and in accordance with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by U.S. GAAP for complete financial statements. In the opinion of management, all adjustments considered necessary for a fair presentation have been included. Results for the three months ended March 31, 2019 are not necessarily indicative of the results that may be expected for the year ended December 31, 2019 . The unaudited condensed consolidated financial statements include the accounts of Aspen Holdings and its subsidiaries. All intercompany transactions and balances have been eliminated on consolidation. The balance sheet as at December 31, 2018 has been derived from the audited consolidated financial statements at that date, but does not include all of the information and footnotes required by U.S. GAAP for complete financial statements. These unaudited condensed consolidated financial statements and notes thereto should be read in conjunction with the consolidated financial statements and notes thereto for the year ended December 31, 2018 contained in the Company’s Annual Report on Form 10-K filed with the SEC on February 13, 2019 (File No. 001-31909). Assumptions and estimates made by management have a significant effect on the amounts reported within the unaudited condensed consolidated financial statements. The most significant of these assumptions and estimates relate to losses and loss adjustment expenses, reinsurance recoverables, gross written premiums and commissions which have not been reported to the Company such as those relating to proportional treaty reinsurance contracts, unrecognized tax benefits, the fair value of derivatives and the fair value of other investments. All material assumptions and estimates are regularly reviewed and adjustments made as necessary, but actual results could differ significantly from those expected when the assumptions or estimates were made. Accounting Pronouncements Adopted in 2019 On February 25, 2016, the Financial Accounting Standards Board (“FASB”) issued ASU 2016-2, “ Leases (Topic 842) ” which supersedes the leases requirements in Topic 840 and establishes the principles that lessees and lessors shall apply to report useful information to users of financial statements about the amount, timing, and uncertainty of cash flows arising from a lease. On July 30, 2018, the FASB issued ASU 2018-11, “ Targeted Improvements (Topic 842)” which amended the transitional guidance of ASU 2016-2, “ Leases (Topic 842)” and provided an alternative transition method to the existing modified retrospective method. In particular, the amendment allows entities to initially apply the new lease standard as at the adoption date and recognize a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. ASU 2018-11 was effective for fiscal years beginning after December 15, 2018, aligned to the effective date and transition requirements of ASU 2016-2. Following the adoption of ASU 2016-02 and ASU 2018-11, the Company recognized right-of-use operating leased assets of $91.2 million , consisting of leased office real estate and motor vehicles, and an operating lease liability of $93.6 million on the balance sheet as of January 1, 2019, and a cumulative effect adjustment of $2.4 million through opening retained earnings. The interest rate assumption applied in determining the present value of future cash flows of 5% was determined based on the Company’s weighted average incremental borrowing rate. During the quarter ended March 31, 2019, additional right-of-use operating leased assets and a corresponding operating lease liability of $3.1 million have been recognized on balance sheet for new or renewed lease agreements. An operating lease charge of $4.5 million was incurred during the quarter, consisting of an amortization charge of $3.3 million on right-of-use operating leases assets and a $1.2 million finance charge on the operating lease liability. On March 5, 2019, the FASB issued ASU 2019-01, “ Codification Improvements (Topic 842)” which amended lessor accounting guidance in ASC 842 and clarifies exemption from certain interim period transitional disclosure requirements. The amendments of this ASU are effective for fiscal years beginning after December 15, 2018. Adoption of this ASU did not have a material impact on the Company’s financial statements and disclosures. On August 28, 2017, the FASB issued ASU 2017-12, “Derivatives and Hedging (Topic 815)” enabling entities to better align their hedge accounting and risk management activities, while also simplifying the application of hedge accounting in certain situations. This ASU is effective for fiscal years beginning after 15 December, 2018 using a modified retrospective approach for cash flow and net investment hedge relationships that exist on the date of adoption. Adoption of this ASU did not have a material impact on the Company’s financial statements and disclosures. On February 14, 2018, the FASB issued ASU 2018-02, “ Income Statement - Reporting Comprehensive Income (Topic 220)” which allows a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act. This ASU is effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years. Adoption of this ASU did not have a material impact on the Company's financial statements and disclosures. On June 20, 2018, the FASB issued ASU 2018-07, “ Compensation - Stock Compensation (Topic 718)” which amends the scope of Topic 718 via improvements to non-employee share-based payment accounting. Amendments include allowing companies to account for share-based payment transactions with non-employees in the same way as share-based payment transactions with employees and includes elections that offer relief to non-public companies when measuring non-employee equity share options. This ASU is effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years. Adoption of this ASU did not have a material impact on the Company's financial statements and disclosures. 2019 Accounting Pronouncements Not Yet Adopted Other accounting pronouncements issued during the three months ended March 31, 2019 were either not relevant to the Company or did not impact the Company’s consolidated financial statements.

Reclassifications from Accumula

Reclassifications from Accumulated Other Comprehensive Income	3 Months Ended
	Mar. 31, 2019
Equity [Abstract]
Reclassifications from Accumulated Other Comprehensive Income	Reclassifications from Accumulated Other Comprehensive Income The following tables set out the components of the Company’s accumulated other comprehensive income (“AOCI”) that are reclassified into the unaudited condensed consolidated statement of operations for the three months ended March 31, 2019 and 2018 : Amount Reclassified from AOCI Details about the AOCI Components Three Months Ended March 31, 2019 Three Months Ended March 31, 2018 Affected Line Item in the Unaudited ($ in millions) Available for sale securities: Realized gains on sale of securities $ 3.0 $ 2.0 Realized and unrealized investment gains Realized (losses) on sale of securities (3.2 ) (1.9 ) Realized and unrealized investment losses (0.2 ) 0.1 Income from operations before income tax Tax on net realized (losses) on securities — (0.1 ) Income tax benefit/(expense) $ (0.2 ) $ — Net income Realized derivatives: Net realized gains on settled derivatives $ 0.4 $ 1.7 General, administrative and corporate expenses Tax on settled derivatives (0.1 ) (0.3 ) Income tax benefit/(expense) $ 0.3 $ 1.4 Net income Total reclassifications from AOCI to the statement of operations, net of income tax $ 0.1 $ 1.4 Net income

Dividends

Dividends	3 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
Dividends	Dividends Dividends. On May 1, 2019, the Company’s Board of Directors (the “Board of Directors”) declared the following quarterly dividends: Dividend Payable on: Record Date: 5.95% preference shares $ 0.3719 July 1, 2019 June 15, 2019 5.625% preference shares $ 0.3516 July 1, 2019 June 15, 2019

Segment Reporting

Segment Reporting	3 Months Ended
	Mar. 31, 2019
Segment Reporting [Abstract]
Segment Reporting	Segment Reporting The Company has two reporting business segments: Insurance and Reinsurance. The Company has determined its reportable segments, Aspen Insurance and Aspen Reinsurance, by taking into account the manner in which management makes operating decisions and assesses operating performance. Profit or loss for each of the Company’s business segments is measured by underwriting profit or loss. Underwriting profit is the excess of net earned premiums over the sum of losses and loss expenses, amortization of deferred policy acquisition costs and general and administrative expenses. Underwriting profit or loss provides a basis for management to evaluate the business segment’s underwriting performance. The Company uses underwriting ratios as measures of performance. The loss ratio is the ratio of losses and loss adjustment expenses to net earned premiums. The policy acquisition expense ratio is the ratio of amortization of deferred policy acquisition costs to net earned premiums. The general and administrative expense ratio is the ratio of general, administrative and corporate expenses to net earned premiums. The combined ratio is the sum of the loss ratio, the policy acquisition expense ratio and the general and administrative expense ratio. Reinsurance Segment. The reinsurance segment consists of property catastrophe reinsurance, other property reinsurance, casualty reinsurance and specialty reinsurance. ACM forms part of our property catastrophe reinsurance line of business as it focuses primarily on property catastrophe business through the use of alternative capital. For a more detailed description of this business segment, see Part I, Item 1, “Business — Business Segments — Reinsurance” in the Company’s 2018 Annual Report on Form 10-K filed with the SEC. Insurance Segment. The insurance segment consists of property and casualty insurance, marine, aviation and energy insurance and financial and professional lines insurance. For a more detailed description of this business segment, see Part I, Item 1 “Business — Business Segments — Insurance” in the Company’s 2018 Annual Report on Form 10-K filed with the SEC. Non-underwriting Disclosures. The Company has provided additional disclosures for corporate and other (non-operating) income and expenses. Corporate and other income and expenses include net investment income, net realized and unrealized investment gains or losses, expenses associated with managing the Group, certain strategic and non-recurring costs, changes in fair value of derivatives and changes in fair value of the loan notes issued by variable interest entities, interest expenses, net realized and unrealized foreign exchange gains or losses, and income taxes, none of which are allocated to the business segments. Corporate expenses are not allocated to the Company’s business segments as they typically do not fluctuate with the levels of premiums written and are not directly related to the Company’s business segment operations. The Company does not allocate its assets by business segment as it evaluates underwriting results of each business segment separately from the results of the Company’s investment portfolio. The following tables provide a summary of gross and net written and earned premiums, underwriting results, ratios and reserves for each of the Company’s business segments for the three months ended March 31, 2019 and 2018 : Three Months Ended March 31, 2019 Reinsurance Insurance Total ($ in millions) Underwriting Revenues Gross written premiums $ 538.4 $ 475.4 $ 1,013.8 Net written premiums 395.6 222.0 617.6 Gross earned premiums 336.5 480.5 817.0 Net earned premiums 276.9 233.7 510.6 Underwriting Expenses Losses and loss adjustment expenses 165.8 146.0 311.8 Amortization of deferred policy acquisition costs 62.6 25.6 88.2 General and administrative expenses 27.2 59.0 86.2 Underwriting income $ 21.3 $ 3.1 24.4 Corporate expenses (11.9 ) Non-operating expenses (1) (39.2 ) Net investment income 51.5 Realized and unrealized investment gains 42.0 Realized and unrealized investment losses (6.2 ) Change in fair value of loan notes issued by variable interest entities (1.5 ) Change in fair value of derivatives (53.3 ) Interest expense on long term debt (5.5 ) Net realized and unrealized foreign exchange gains 5.1 Other income 1.7 Other expenses (0.9 ) Income before tax $ 6.2 Net reserves for loss and loss adjustment expenses $ 2,871.5 $ 2,005.9 $ 4,877.4 Ratios Loss ratio 59.9 % 62.5 % 61.1 % Policy acquisition expense ratio 22.6 11.0 17.3 General and administrative expense ratio 9.8 25.2 26.9 (2) Expense ratio 32.4 36.2 44.2 Combined ratio 92.3 % 98.7 % 105.3 % (1) Non-operating expenses includes $6.1 million of expenses related to the Company’s operating effectiveness and efficiency program (the “Effectiveness and Efficiency Program”) and $29.8 million of fees related to or triggered by the Merger. (2) The general and administrative expense ratio in the “Total” column includes corporate and non-operating expenses. Three Months Ended March 31, 2018 Reinsurance Insurance Total ( $ in millions) Underwriting Revenues Gross written premiums $ 623.5 $ 493.3 $ 1,116.8 Net written premiums 425.0 210.5 635.5 Gross earned premiums 375.0 467.6 842.6 Net earned premiums 282.5 251.0 533.5 Underwriting Expenses Losses and loss adjustment expenses 166.9 143.3 310.2 Amortization of deferred policy acquisition costs 55.9 34.9 90.8 General and administrative expenses 31.6 63.6 95.2 Underwriting income $ 28.1 $ 9.2 37.3 Corporate expenses (13.7 ) Non-operating expenses (1) (12.1 ) Net investment income 47.3 Realized and unrealized investment gains 100.6 Realized and unrealized investment losses (138.3 ) Change in fair value of loan notes issued by variable interest entities 1.0 Change in fair value of derivatives 23.5 Interest expense on long term debt (7.4 ) Net realized and unrealized foreign exchange (losses) (4.7 ) Other income 2.1 Other expenses (1.2 ) Income before tax $ 34.4 Net reserves for loss and loss adjustment expenses $ 2,823.6 $ 2,244.5 $ 5,068.1 Ratios Loss ratio 59.1 % 57.1 % 58.1 % Policy acquisition expense ratio 19.8 13.9 17.0 General and administrative expense ratio 11.2 25.3 22.7 (2) Expense ratio 31.0 39.2 39.7 Combined ratio 90.1 % 96.3 % 97.8 % (1) Non-operating expenses includes $11.8 million of expenses related to the Company’s Effectiveness and Efficiency Program. (2) The general and administrative expense ratio in the “Total” column includes corporate and non-operating expenses.

Investments

Investments	3 Months Ended
	Mar. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Investments	Investments Statements of Operations and Other Comprehensive Income Investment Income. The following table summarizes investment income for the three months ended March 31, 2019 and 2018 : For the Three Months Ended March 31, 2019 March 31, 2018 ($ in millions) Fixed income securities — Available for sale $ 34.3 $ 33.3 Fixed income securities — Trading 11.7 12.0 Short-term investments — Available for sale 0.8 0.2 Short-term investments — Trading 0.2 0.2 Fixed term deposits (included in cash and cash equivalents) 4.5 2.4 Equity securities — Trading — 1.2 Catastrophe bonds — Trading 0.8 0.6 Other investments, at fair value 1.4 — Total $ 53.7 $ 49.9 Investment expenses (2.2 ) (2.6 ) Net investment income $ 51.5 $ 47.3 The following table summarizes the net realized and unrealized investment gains and losses recorded in the statement of operations and the change in unrealized gains and losses on investments recorded in other comprehensive income for the three months ended March 31, 2019 and 2018 : For the Three Months Ended March 31, 2019 March 31, 2018 ($ in millions) Available for sale: Fixed income securities — gross realized gains $ 3.0 $ 1.8 Fixed income securities — gross realized (losses) (3.2 ) (1.8 ) Cash and cash equivalents — gross realized gains — 0.2 Cash and cash equivalents — gross realized (losses) — (0.1 ) Trading: Fixed income securities — gross realized gains 2.3 1.6 Fixed income securities — gross realized (losses) (2.8 ) (7.0 ) Short-term investments — gross realized (losses) (0.1 ) — Cash and cash equivalents — gross realized gains 0.1 1.6 Equity securities — gross realized gains — 94.5 Equity securities — gross realized (losses) — (20.3 ) Catastrophe bonds — net unrealized gains 0.3 0.9 Net change in gross unrealized gains/(losses) 36.3 (108.8 ) Investments — equity method: Gross realized and unrealized (loss) in MVI — (0.1 ) Gross realized and unrealized (loss) in Bene (0.1 ) (0.2 ) Total net realized and unrealized investment gains/(losses) recorded in the statement of operations $ 35.8 $ (37.7 ) Change in available for sale net unrealized gains/(losses): Fixed income securities 75.6 (82.9 ) Change in taxes (5.2 ) 5.5 Total change in net unrealized gains/(losses), net of taxes, recorded in other comprehensive income $ 70.4 $ (77.4 ) Balance Sheet Fixed Income Securities and Short-Term Investments — Available For Sale. The following tables present the cost or amortized cost, gross unrealized gains and losses and estimated fair market value of available for sale investments in fixed income securities and short-term investments as at March 31, 2019 and December 31, 2018 : As at March 31, 2019 Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Market Value ($ in millions) U.S. government $ 1,352.6 $ 14.6 $ (8.0 ) $ 1,359.2 U.S. agency 39.3 0.3 (0.1 ) 39.5 Municipal 46.5 1.9 (0.2 ) 48.2 Corporate 2,151.6 21.8 (10.8 ) 2,162.6 Non-U.S. government-backed corporate 98.1 0.4 (0.2 ) 98.3 Non-U.S. government 356.9 4.9 (0.2 ) 361.6 Asset-backed 16.2 — (0.1 ) 16.1 Agency mortgage-backed 955.3 9.9 (10.2 ) 955.0 Total fixed income securities — Available for sale 5,016.5 53.8 (29.8 ) 5,040.5 Total short-term investments — Available for sale 160.7 0.2 — 160.9 Total $ 5,177.2 $ 54.0 $ (29.8 ) $ 5,201.4 As at December 31, 2018 Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Market Value ($ in millions) U.S. government $ 1,413.5 $ 6.8 $ (16.1 ) $ 1,404.2 U.S. agency 47.7 0.1 (0.4 ) 47.4 Municipal 46.7 1.3 (0.8 ) 47.2 Corporate 2,238.9 7.8 (40.5 ) 2,206.2 Non-U.S. government-backed corporate 93.2 0.2 (0.2 ) 93.2 Non-U.S. government 399.8 3.6 (0.8 ) 402.6 Asset-backed 17.4 — (0.1 ) 17.3 Agency mortgage-backed 1,025.1 6.5 (19.0 ) 1,012.6 Total fixed income securities — Available for sale 5,282.3 26.3 (77.9 ) 5,230.7 Total short-term investments — Available for sale 105.6 — — 105.6 Total $ 5,387.9 $ 26.3 $ (77.9 ) $ 5,336.3 Fixed Income Securities, Short-Term Investments, Equities and Catastrophe Bonds — Trading. The following tables present the cost or amortized cost, gross unrealized gains and losses, and estimated fair market value of trading investments in fixed income securities, short-term investments, equity securities and catastrophe bonds as at March 31, 2019 and December 31, 2018 : As at March 31, 2019 Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Market Value ($ in millions) U.S. government $ 217.4 $ 1.6 $ (0.2 ) $ 218.8 Municipal 3.0 — — 3.0 Corporate 754.9 12.4 (3.4 ) 763.9 Non-U.S. government 246.4 6.8 (0.7 ) 252.5 Asset-backed 2.3 — — 2.3 Agency mortgage-backed 49.1 0.3 (0.6 ) 48.8 Total fixed income securities — Trading 1,273.1 21.1 (4.9 ) 1,289.3 Total short-term investments — Trading 81.0 — — 81.0 Total catastrophe bonds — Trading 39.5 — (1.4 ) 38.1 Total $ 1,393.6 $ 21.1 $ (6.3 ) $ 1,408.4 As at December 31, 2018 Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Market Value ($ in millions) U.S. government $ 146.6 $ 1.6 $ (0.5 ) $ 147.7 Municipal 2.8 — (0.1 ) 2.7 Corporate 734.2 2.6 (16.6 ) 720.2 Non-U.S. government 268.7 1.9 (5.2 ) 265.4 Asset-backed 2.4 — — 2.4 Agency mortgage-backed 50.3 0.2 (1.1 ) 49.4 Total fixed income securities — Trading 1,205.0 6.3 (23.5 ) 1,187.8 Total short-term investments — Trading 9.5 — — 9.5 Total catastrophe bonds — Trading 37.9 0.1 (1.8 ) 36.2 Total $ 1,252.4 $ 6.4 $ (25.3 ) $ 1,233.5 The Company classifies the financial instruments presented in the tables above as held for trading as this most closely reflects the facts and circumstances of the investments held. Catastrophe Bonds. The Company has invested in catastrophe bonds with a total value of $38.1 million as at March 31, 2019 . The bonds are either zero-coupon notes or receive quarterly interest payments based on variable interest rates with scheduled maturities ranging from 2019 to 2021. The redemption value of the bonds will adjust based on the occurrence or aggregate occurrence of a covered event, such as windstorms and earthquakes in the United States, Canada, the North Atlantic, South America, Europe, Japan or Australia. Investments — Equity Method. In January 2015, the Company established, along with seven other insurance companies, a micro-insurance venture consortium and micro-insurance incubator (“MVI”) domiciled in Bermuda. The MVI is a social impact organization that provides micro-insurance products to assist global emerging consumers. The Company’s initial investment in the MVI was $0.8 million . The Company made an additional investment of $0.1 million in the twelve months ended December 31, 2017 and a further investment of $0.1 million in the twelve months ended December 31, 2018. On July 26, 2016, the Company purchased through its wholly-owned subsidiary, Acorn Limited (“Acorn”), a 20% share of Bene Assicurazioni (“Bene”), an Italian-based motor insurer for a total consideration of $3.3 million . The investment is accounted for under the equity method and adjustments to the carrying value of this investment are made based on the Company’s share of capital, including share of income and expenses. The Company made an additional investment of $1.2 million in the twelve months ended December 31, 2018. On January 1, 2017, the Company purchased through its wholly-owned subsidiary, Aspen U.S. Holdings, Inc. (“Aspen U.S. Holdings”), a 49% share of Digital Risk Resources, LLC (“Digital Re”), a U.S.-based enterprise engaged in the business of developing, marketing and servicing turnkey information security and privacy liability insurance products, for a total consideration of $2.3 million . The investment is accounted for under the equity method and adjustments to the carrying value of this investment are made based on the Company’s share of capital, including share of income and expenses. On December 18, 2017, the Company acquired through its wholly-owned subsidiary, Aspen U.S. Holdings, a 23.2% share of Crop Re Services LLC (“Crop Re”), a newly formed U.S.-based subsidiary of CGB Diversified Services, Inc (“CGB DS”) in exchange for the sale of AG Logic Holdings, LLC (“AgriLogic”), the Company’s former U.S. crop insurance business. Total consideration for the sale of AgriLogic consisted of the 23.2% share of Crop Re valued at $62.5 million and cash in the amount of $5.9 million . Crop Re is responsible for directing the placement of reinsurance on behalf of CGB DS and CGB Insurance Company (“CGBIC”), an Indiana insurance company affiliate of CGB DS and an RMA licensed crop insurer. The remaining 76.8% of Crop Re is owned by CGB DS. AAIC’s primary crop insurance coverage will be run-off and AAIC, or an affiliate of AAIC, will provide quota share reinsurance to CGBIC for both federal and state regulated crop insurance as part of Aspen’s ownership in Crop Re. The investment in Crop Re represents the Company’s share of the net assets of Crop Re plus the difference between the cost of the investment and the amount of underlying equity in net assets, the basis difference. The Company has determined that this basis difference of $62.5 million represents the value attributable to the ability of Crop Re to direct the placement of reinsurance business under the reinsurance commitment contained within the operating agreement between Crop Re and the Company. The investment in Crop Re is accounted for under the equity method and adjustments to the carrying value of this investment are made based on the Company’s share of capital, including share of income and expenses. On September 18, 2018, Aspen U.S. Holdings sold a 60% interest in AgriLogic Consulting, LLC, its agricultural consulting business, to CGB DS and an individual investor. The Company’s residual 40% interest in AgriLogic Consulting, LLC, is valued at $ Nil . The table below shows the Company’s investments in the MVI, Bene, Digital Re and Crop Re for the three months ended March 31, 2019 : For the Three Months Ended March 31, 2019 MVI Bene Digital Re Crop Re Total ($ in millions) Opening undistributed value of investment $ 0.5 $ 3.2 $ 0.9 $ 62.5 $ 67.1 Investment in the period — — — — — Realized/unrealized losses for the three months to March 31, 2019 — (0.1 ) — — (0.1 ) Closing undistributed value of investment $ 0.5 $ 3.1 $ 0.9 $ 62.5 $ 67.0 Other Investments. On December 20, 2017, the Company committed $100.0 million as a limited partner to a real estate fund. The investment objective of the fund is to achieve attractive risk-adjusted returns through the acquisition of income producing, high quality assets in gateway cities located in the U.S. and Canada in the office, retail, industrial and multifamily sectors of the real estate market. On May 1, 2018, the Company received a demand for an initial capital call of $86.2 million and paid the capital call on May 10, 2018. On September 19, 2018, the Company received a demand for the final capital call of $13.8 million and paid the capital on September 28, 2018. For further information, refer to Note 17 in these unaudited condensed consolidated financial statements. Fixed Income Securities. The scheduled maturity distribution of available for sale fixed income securities as at March 31, 2019 and December 31, 2018 is set forth in the tables below. Actual maturities may differ from contractual maturities because issuers of securities may have the right to call or prepay obligations with or without call or prepayment penalties. As at March 31, 2019 Amortized Cost or Cost Fair Market Value Average S&P Ratings by Maturity ($ in millions) Due one year or less $ 441.1 $ 440.7 AA- Due after one year through five years 2,463.8 2,467.0 AA- Due after five years through ten years 1,014.7 1,025.1 AA- Due after ten years 125.4 136.6 AA- Subtotal 4,045.0 4,069.4 Agency mortgage-backed 955.3 955.0 AA+ Asset-backed 16.2 16.1 AAA Total fixed income securities — Available for sale $ 5,016.5 $ 5,040.5 As at December 31, 2018 Amortized Cost or Cost Fair Market Value Average S&P Ratings by Maturity ($ in millions) Due one year or less $ 464.3 $ 463.5 AA- Due after one year through five years 2,605.7 2,582.0 AA- Due after five years through ten years 1,047.9 1,028.3 AA- Due after ten years 121.9 127.0 AA- Subtotal 4,239.8 4,200.8 Agency mortgage-backed 1,025.1 1,012.6 AA+ Asset-backed 17.4 17.3 AAA Total fixed income securities — Available for sale $ 5,282.3 $ 5,230.7 Guaranteed Investments. The Company held no investments which were guaranteed by mono-line insurers, excluding those with explicit government guarantees as at March 31, 2019 and December 31, 2018 . The Company’s exposure to other third-party guaranteed debt was primarily to investments backed by non-U.S. government guaranteed issuers. Gross Unrealized Loss. The following tables summarize, by type of security, the aggregate fair value and gross unrealized loss by length of time the security has been in an unrealized loss position in the Company’s available for sale portfolio as at March 31, 2019 and December 31, 2018 : As at March 31, 2019 0-12 months Over 12 months Total Fair Market Value Gross Unrealized Loss Fair Market Value Gross Unrealized Loss Fair Market Value Gross Unrealized Loss Number of Securities ($ in millions) U.S. government $ 90.9 $ (0.2 ) $ 645.1 $ (7.8 ) $ 736.0 $ (8.0 ) 75 U.S. agency 1.4 — 14.8 (0.1 ) 16.2 (0.1 ) 7 Municipal — — 25.4 (0.2 ) 25.4 (0.2 ) 8 Corporate 27.8 (0.1 ) 966.9 (10.7 ) 994.7 (10.8 ) 380 Non-U.S. government-backed corporate — — 28.1 (0.2 ) 28.1 (0.2 ) 10 Non-U.S. government 5.7 — 53.2 (0.2 ) 58.9 (0.2 ) 35 Asset-backed — — 13.1 (0.1 ) 13.1 (0.1 ) 6 Agency mortgage-backed 28.5 (0.1 ) 496.6 (10.1 ) 525.1 (10.2 ) 197 Total fixed income securities — Available for sale 154.3 (0.4 ) 2,243.2 (29.4 ) 2,397.5 (29.8 ) 718 Total short-term investments — Available for sale 17.2 — — — 17.2 — 7 Total $ 171.5 $ (0.4 ) $ 2,243.2 $ (29.4 ) $ 2,414.7 $ (29.8 ) 725 As at December 31, 2018 0-12 months Over 12 months Total Fair Market Value Gross Unrealized Loss Fair Market Value Gross Unrealized Loss Fair Market Value Gross Unrealized Loss Number of Securities ($ in millions) U.S. government $ 180.2 $ (0.7 ) $ 740.6 $ (15.4 ) $ 920.8 $ (16.1 ) 103 U.S. agency 13.5 (0.2 ) 18.4 (0.2 ) 31.9 (0.4 ) 12 Municipal 3.1 (0.1 ) 25.0 (0.7 ) 28.1 (0.8 ) 9 Corporate 999.1 (15.2 ) 762.2 (25.3 ) 1,761.3 (40.5 ) 667 Non-U.S. government-backed corporate 14.5 — 25.8 (0.2 ) 40.3 (0.2 ) 12 Non-U.S. government 64.0 (0.3 ) 91.0 (0.5 ) 155.0 (0.8 ) 57 Asset-backed 6.3 — 10.8 (0.1 ) 17.1 (0.1 ) 8 Agency mortgage-backed 245.7 (2.6 ) 447.3 (16.4 ) 693.0 (19.0 ) 253 Total fixed income securities — Available for sale 1,526.4 (19.1 ) 2,121.1 (58.8 ) 3,647.5 (77.9 ) 1,121 Total short-term investments — Available for sale 34.5 — — — 34.5 — 12 Total $ 1,560.9 $ (19.1 ) $ 2,121.1 $ (58.8 ) $ 3,682.0 $ (77.9 ) 1,133 Other-Than-Temporary Impairments. A security is potentially impaired when its fair value is below its amortized cost. The Company reviews its available for sale fixed income portfolios on an individual security basis for potential other-than-temporary impairment (“OTTI”) each quarter based on criteria including issuer-specific circumstances, credit ratings actions and general macro-economic conditions. The total OTTI charge for the three months ended March 31, 2019 was $ Nil ( March 31, 2018 —$ Nil ). For a more detailed description of accounting policies for OTTI, please refer to Note 2(c) of the “Notes to the Audited Consolidated Financial Statements” in the Company’s 2018 Annual Report on Form 10-K filed with the SEC.

Variable Interest Entities

Variable Interest Entities	3 Months Ended
	Mar. 31, 2019
Payables and Accruals [Abstract]
Variable Interest Entities	Variable Interest Entities As at March 31, 2019 , the Company had investments in two variable interest entities (“VIE”): Peregrine Reinsurance Ltd (“Peregrine”) and Silverton Re Ltd (“Silverton”). Peregrine. In November 2016, the Company, registered Peregrine as a segregated accounts company under the Bermuda Segregated Accounts Companies Act 2000, as amended. As at March 31, 2019 , Peregrine had four segregated accounts which were funded by a third party investor. The segregated accounts have not been consolidated as part of the Company’s consolidated financial statements. The Company has, however, determined that Peregrine has the characteristics of a VIE as addressed by the guidance in ASC 810, Consolidation . The Company concluded that it is not the primary beneficiary of the four segregated accounts of Peregrine but is the primary beneficiary of the Peregrine general fund and, similar to prior reporting periods, the Company has included the results of the Peregrine general fund in its consolidated financial statements. The Company’s exposure to Peregrine’s general fund is not material. Silverton. On September 10, 2013, the Company established Silverton, a Bermuda domiciled special purpose insurer formed to provide additional collateralized capacity to support Aspen Re’s business through retrocession agreements which are collateralized and funded by Silverton through the issuance of one or more series of participating loan notes (collectively, the “Loan Notes”). Silverton is a non-rated insurer and the risks are fully collateralized by way of funds held in trust for the benefit of Aspen Bermuda and Aspen U.K., the ceding reinsurers. Silverton was not renewed in 2017 and has not issued any Loan Notes since, in the future, any such quota share support for Aspen Re will be provided by a separate cell of Peregrine. All proceeds from the issuance of the Loan Notes were deposited into separate collateral accounts for each series of Loan Notes to fund Silverton’s obligations under a retrocession property quota share agreement entered into with Aspen Bermuda or Aspen Bermuda and Aspen U.K., as the case may be. The holders of the Loan Notes participate in any profit or loss generated by Silverton attributable to the operations of the respective Silverton segregated account. Any existing value of the Loan Notes will be returned to the noteholders in installments after the expiration of the risk period of the retrocession agreement issued by Silverton for the related series of Loan Notes with the final payment being contractually due on the respective maturity dates. The following tables show the total liability balance of the Loan Notes for the three months ended March 31, 2019 and 2018 : For the Three Months Ended March 31, 2019 Third Party Aspen Holdings Total ($ in millions) Opening balance $ 4.6 $ 20.6 $ 25.2 Total change in fair value for the period 1.5 0.4 1.9 Total distributed in the period (0.2 ) (19.6 ) (19.8 ) Closing balance as at March 31, 2019 $ 5.9 $ 1.4 $ 7.3 Liability Loan notes (long-term liabilities) $ — $ — $ — Accrued expenses (current liabilities) 5.9 1.4 7.3 Total aggregate unpaid balance as at March 31, 2019 $ 5.9 $ 1.4 $ 7.3 For the Three Months Ended March 31, 2018 Third Party Aspen Holdings Total ($ in millions) Opening balance $ 86.6 $ 20.6 $ 107.2 Total change in fair value for the period (1.0 ) (0.3 ) (1.3 ) Total distributed in the period (45.8 ) (10.7 ) (56.5 ) Closing balance as at March 31, 2018 $ 39.8 $ 9.6 $ 49.4 Liability Loan notes (long-term liabilities) $ 32.2 $ 7.7 $ 39.9 Accrued expenses (current liabilities) 7.6 1.9 9.5 Total aggregate unpaid balance as at March 31, 2018 $ 39.8 $ 9.6 $ 49.4 The Company has determined that Silverton has the characteristics of a VIE that are addressed by the guidance in ASC 810, Consolidation . The Company concluded that it is the primary beneficiary of Silverton as it owns all of Silverton’s voting shares and issued share capital, and has a significant financial interest and the power to control Silverton. As a result, the Company consolidated Silverton upon its formation. The Company has no other obligation to provide financial support to Silverton and neither the creditors nor beneficial interest holders of Silverton have recourse to the Company’s general credit. In the event of an extreme catastrophic property reinsurance event or severe credit-related event, there is a risk that Aspen Bermuda and Aspen U.K. would be unable to recover losses from Silverton. These two risks are mitigated as follows: i. Silverton has collateralized the aggregate limit provided to Aspen Bermuda and Aspen U.K. by way of a trust in favor of Aspen Bermuda and Aspen U.K. as beneficiaries; ii. the trustee is a large, well-established regulated entity; and iii. all funds within the trust account are bound by investment guidelines restricting investments to one of the institutional class money market funds run by large international investment managers. For further information regarding the Loan Notes attributable to the third-party investments in Silverton, refer to Note 8 of these unaudited condensed consolidated financial statements.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The Company’s estimates of fair value for financial assets and liabilities are based on the framework established in the fair value accounting guidance included in ASC 820, Fair Value Measurements and Disclosures . The framework prioritizes the inputs, which refer broadly to assumptions market participants would use in pricing an asset or liability, into three levels. The Company considers prices for actively traded securities to be derived based on quoted prices in an active market for identical assets, which are Level 1 inputs in the fair value hierarchy. The majority of these securities are valued using prices supplied by index providers. The Company considers prices for other securities that may not be as actively traded which are priced via pricing services, index providers, vendors and broker-dealers, or with reference to interest rates and yield curves, to be derived based on inputs that are observable for the asset, either directly or indirectly, which are Level 2 inputs in the fair value hierarchy. The majority of these securities are also valued using prices supplied by index providers. The Company considers securities, other financial instruments and derivative insurance contracts subject to fair value measurement whose valuation is derived by internal valuation models to be based largely on unobservable inputs, which are Level 3 inputs in the fair value hierarchy. The following tables present the level within the fair value hierarchy at which the Company’s financial assets and liabilities are measured on a recurring basis as at March 31, 2019 and December 31, 2018 : As at March 31, 2019 Level 1 Level 2 Level 3 Total ($ in millions) Available for sale financial assets, at fair value U.S. government $ 1,359.1 $ — $ — $ 1,359.1 U.S. agency — 39.5 — 39.5 Municipal — 48.2 — 48.2 Corporate — 2,162.7 — 2,162.7 Non-U.S. government-backed corporate — 98.3 — 98.3 Non-U.S. government 224.6 137.0 — 361.6 Asset-backed — 16.1 — 16.1 Agency mortgage-backed — 955.0 — 955.0 Total fixed income securities available for sale, at fair value 1,583.7 3,456.8 — 5,040.5 Short-term investments available for sale, at fair value 149.4 11.5 — 160.9 Held for trading financial assets, at fair value U.S. government 218.8 — — 218.8 Municipal — 3.0 — 3.0 Corporate — 763.9 — 763.9 Non-U.S. government 48.9 203.6 — 252.5 Asset-backed — 2.3 — 2.3 Agency mortgage-backed — 48.8 — 48.8 Total fixed income securities trading, at fair value 267.7 1,021.6 — 1,289.3 Short-term investments trading, at fair value 76.8 4.2 — 81.0 Catastrophe bonds trading, at fair value — 38.1 — 38.1 Other investments (1) — — — 104.0 Other financial assets and liabilities, at fair value Derivatives at fair value — foreign exchange contracts — 10.8 — 10.8 Liabilities under derivative contracts — foreign exchange contracts — (7.2 ) — (7.2 ) Liabilities under derivative contracts — interest rate swaps — (49.5 ) — (49.5 ) Loan notes issued by variable interest entities, at fair value (included within accrued expenses and other payables) — — (5.9 ) (5.9 ) Total $ 2,077.6 $ 4,486.3 $ (5.9 ) $ 6,662.0 (1) Other investments represents our investment in a real estate fund and is measured at fair value using the net asset value per share practical expedient. As a result this has not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the condensed consolidated balance sheets. The investment in the real estate fund is subject to restrictions as detailed in Note 17. Transfers of assets into or out of a particular level are recorded at their fair values as of the end of each reporting period, consistent with the date of the determination of fair value. There were no significant transfers between Level 1, Level 2 and Level 3 during the three months ended March 31, 2019 . The Company settled $0.2 million of Level 3 liabilities in respect of the Loan Notes issued by Silverton for the three months ended March 31, 2019 . As at March 31, 2019 , there were no the assets classified as Level 3 and the Company’s Level 3 liabilities consisted solely of the Loan Notes issued by Silverton. As at December 31, 2018 Level 1 Level 2 Level 3 Total ($ in millions) Available for sale financial assets, at fair value U.S. government $ 1,404.2 $ — $ — $ 1,404.2 U.S. agency — 47.4 — 47.4 Municipal — 47.2 — 47.2 Corporate — 2,206.2 — 2,206.2 Non-U.S. government-backed corporate — 93.2 — 93.2 Non-U.S. government 268.0 134.6 — 402.6 Asset-backed — 17.3 — 17.3 Agency mortgage-backed — 1,012.6 — 1,012.6 Total fixed income securities available for sale, at fair value 1,672.2 3,558.5 — 5,230.7 Short-term investments available for sale, at fair value 93.7 11.9 — 105.6 Held for trading financial assets, at fair value U.S. government 147.7 — — 147.7 Municipal — 2.7 — 2.7 Corporate — 720.2 — 720.2 Non-U.S. government 68.2 197.2 — 265.4 Asset-backed — 2.4 — 2.4 Agency mortgage-backed — 49.4 — 49.4 Total fixed income securities trading, at fair value 215.9 971.9 — 1,187.8 Short-term investments trading, at fair value 4.5 5.0 — 9.5 Catastrophe bonds trading, at fair value — 36.2 — 36.2 Other investments (1) — — — 102.5 Other financial assets and liabilities, at fair value Derivatives at fair value – foreign exchange contracts — 14.6 — 14.6 Liabilities under derivative contracts – foreign exchange contracts — (15.1 ) — (15.1 ) Loan notes issued by variable interest entities, at fair value (included within accrued expenses and other payables) — — (4.6 ) (4.6 ) Total $ 1,986.3 $ 4,583.0 $ (4.6 ) $ 6,667.2 (1) Other investments represents our investment in a real estate fund and is measured at fair value using the net asset value per share practical expedient. As a result this has not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the condensed consolidated balance sheets. The investment in the real estate fund is subject to restrictions as detailed in Note 17. Transfers of assets into or out of a particular level are recorded at their fair values as of the end of each reporting period, consistent with the date of the determination of fair value. During the twelve months ended December 31, 2018 , there were no transfers between Level 1, 2 and 3. The Company settled $115.6 million of Level 3 liabilities in respect of the Loan Notes issued by Silverton for the twelve months ended December 31, 2018 . As at December 31, 2018 , there were no assets classified as Level 3 and the Company’s Level 3 liabilities consisted solely of the Loan Notes issued by Silverton. The following table presents a reconciliation of the beginning and ending balances for all assets and liabilities measured at fair value on a recurring basis using Level 3 inputs for the three months ended March 31, 2019 and 2018 : Reconciliation of Liabilities Using Level 3 Inputs Three Months Ended March 31, 2019 Three Months Ended March 31, 2018 ($ in millions) Balance at the beginning of the period $ 4.6 $ 86.6 Distributed to third party (0.2 ) (45.8 ) Total change in fair value included in the statement of operations 1.5 (1.0 ) Balance at the end of the period (1) $ 5.9 $ 39.8 (1) The amount classified within accrued expenses and other payables was $5.9 million and $7.6 million as at March 31, 2019 and March 31, 2018 , respectively. Valuation of Fixed Income Securities . The Company’s fixed income securities are classified as either available for sale or trading and carried at fair value. As at March 31, 2019 and December 31, 2018 , the Company’s fixed income securities were valued by pricing services, index providers or broker-dealers using standard market conventions. The market conventions utilize market quotations, market transactions in comparable instruments and various relationships between instruments including, but not limited to, yield to maturity, dollar prices and spread prices in determining value. Independent Pricing Services and Index Providers. The underlying methodology used to determine the fair value of securities in the Company’s available for sale and trading portfolios by the pricing services and index providers the Company uses is very similar. Pricing services will gather observable pricing inputs from multiple external sources, including buy and sell-side contacts and broker-dealers, in order to develop their internal prices. Index providers are those firms which provide prices for a range of securities within one or more asset classes, typically using their own in-house market makers (traders) as the primary pricing source for the indices, although ultimate valuations may also rely on other observable data inputs to derive a dollar price for all index-eligible securities. Index providers without in-house trading desks will function similarly to a pricing service in that they will gather their observable pricing inputs from multiple external sources. All prices for the Company’s securities attributed to index providers are for an individual security within the respective indices. Pricing services and index providers provide pricing for less complex, liquid securities based on market quotations in active markets. Pricing services and index providers supply prices for a broad range of securities including those for actively traded securities, such as Treasury and other Government securities, in addition to those that trade less frequently or where valuation includes reference to credit spreads, pay down and pre-pay features and other observable inputs. These securities include Government Agency, Municipals, Corporate and Asset-Backed Securities. For securities that may trade less frequently or do not trade on a listed exchange, these pricing services and index providers may use matrix pricing consisting of observable market inputs to estimate the fair value of a security. These observable market inputs include: reported trades, benchmark yields, broker-dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, reference data, and industry and economic factors. Additionally, pricing services and index providers may use a valuation model such as an option adjusted spread model commonly used for estimating fair values of mortgage-backed and asset-backed securities. Neither the Company, nor its index providers, derives dollar prices using an index as a pricing input for any individual security. Broker-Dealers. The Company obtains quotes from broker-dealers who are active in the corresponding markets when prices are unavailable from independent pricing services or index providers. Generally, broker-dealers value securities through their trading desks based on observable market inputs. Their pricing methodologies include mapping securities based on trade data, bids or offers, observed spreads and performance of newly issued securities. They may also establish pricing through observing secondary trading of similar securities. The Company obtains prices for all of its fixed income investment securities via its third-party accounting service provider, and in the majority of cases receiving a number of quotes so as to obtain the most comprehensive information available to determine a security’s fair value. A single valuation is applied to each security based on the vendor hierarchy maintained by the Company’s third-party accounting service provider. As at March 31, 2019 the Company obtained an average of 2.2 quotes per fixed income investment compared to 2.0 quotes as at December 31, 2018 . Pricing sources used in pricing fixed income investments as at March 31, 2019 and December 31, 2018 were as follows: As at March 31, 2019 As at December 31, 2018 Index providers 84 % 84 % Pricing services 14 13 Broker-dealers 2 3 Total 100 % 100 % Summary Pricing Information Table. A summary of securities priced using pricing information from index providers as at March 31, 2019 and December 31, 2018 is provided below: As at March 31, 2019 As at December 31, 2018 Fair Market Value Determined using Prices from Index Providers % of Total Fair Value by Security Type Fair Market Value Determined using Prices from Index Providers % of Total Fair Value by Security Type ($ in millions, except for percentages) U.S. government $ 1,577.9 100 % $ 1,551.9 100 % U.S. agency 38.3 97 % 45.7 96 % Municipal 15.5 30 % 14.7 30 % Corporate 2,755.9 94 % 2,775.7 95 % Non-U.S. government-backed corporate 44.1 45 % 43.3 47 % Non-U.S. government 368.2 60 % 366.1 56 % Asset-backed 7.8 42 % 7.7 39 % Agency mortgage-backed 532.2 53 % 567.5 53 % Total fixed income securities $ 5,339.9 84 % $ 5,372.6 84 % The Company, in conjunction with its third-party accounting service provider, obtains an understanding of the methods, models and inputs used by the third-party pricing service and index providers to assess the ongoing appropriateness of vendors’ prices. The Company and its third-party accounting service provider also have controls in place to validate that amounts provided represent fair values. Processes to validate and review pricing include, but are not limited to: • quantitative analysis (e.g., comparing the quarterly return for each managed portfolio to its target benchmark, with significant differences identified and investigated); • comparison of market values obtained from pricing services, index providers and broker-dealers against alternative price sources for each security where further investigation is completed when significant differences exist for pricing of individual securities between pricing sources; • initial and ongoing evaluation of methodologies used by outside parties to calculate fair value; and • comparison of the fair value estimates to the Company’s knowledge of the current market. Prices obtained from pricing services, index providers and broker-dealers are not adjusted by us; however, prices provided by a pricing service, index provider or broker-dealer in certain instances may be challenged based on information available from market or internal sources, including those available to the Company’s third-party investment accounting service provider. Subsequent to any challenge, revisions made by the pricing service, index provider or broker-dealer to the quotes are supplied to the Company’s investment accounting service provider. Management reviews the vendor hierarchy maintained by the Company’s third-party accounting service provider in order to determine which price source provides the most appropriate fair value (i.e., a price obtained from a pricing service with more seniority in the hierarchy will be used over a less senior one in all cases). The hierarchy level assigned to each security in the Company’s available for sale and trading portfolios is based upon its assessment of the transparency and reliability of the inputs used in the valuation as of the measurement date. The hierarchy of index providers and pricing services is determined using various qualitative and quantitative points arising from reviews of the vendors conducted by the Company’s third-party accounting service provider. Vendor reviews include annual onsite due diligence meetings with index providers and pricing services vendors covering valuation methodology, operational walkthroughs and legal and compliance updates. Index providers are assigned the highest priority in the pricing hierarchy due primarily to availability and reliability of pricing information. Fixed Income Securities . The Company’s fixed income securities are traded on the over-the-counter (“OTC”) market based on prices provided by one or more market makers in each security. Securities such as U.S. Government, U.S. Agency, Non-U.S. Government and investment grade corporate bonds have multiple market makers in addition to readily observable market value indicators such as expected credit spread, except for Treasury securities, over the yield curve. The Company uses a variety of pricing sources to value fixed income securities including those securities that have pay down/prepay features such as mortgage-backed securities and asset-backed securities in order to ensure fair and accurate pricing. The fair value estimates for the investment grade securities in the Company’s portfolio do not use significant unobservable inputs or modeling techniques. U.S. Government and Agency. U.S. government and agency securities consist primarily of bonds issued by the U.S. Treasury and corporate debt issued by agencies such as the Federal National Mortgage Association (“FNMA”), the Federal Home Loan Mortgage Corporation (“FHLMC”) and the Federal Home Loan Bank. As the fair values of U.S. Treasury securities are based on unadjusted market prices in active markets, they are classified within Level 1. The fair values of U.S. government agency securities are priced using the spread above the risk-free yield curve. As the yields for the risk-free yield curve and the spreads for these securities are observable market inputs, the fair values of U.S. government agency securities are classified within Level 2. Municipals. The Company’s municipal portfolio comprises bonds issued by U.S. domiciled state and municipality entities. The fair value of these securities is determined using spreads obtained from broker-dealers, trade prices and the new issue market which are Level 2 inputs in the fair value hierarchy. Consequently, these securities are classified within Level 2. Foreign Government. The issuers for securities in this category are non-U.S. governments and their agencies. The fair values of certain non-U.S. government bonds, primarily sourced from international indices, are based on unadjusted market prices in active markets and are therefore classified within Level 1. The remaining non-U.S government bonds are classified within Level 2 as they are not as actively traded. The fair values of the non-U.S. agency securities, again primarily sourced from international indices, are priced using the spread above the risk-free yield curve. As the yields for the risk-free yield curve and the spreads for these securities are observable market inputs, the fair values of non-U.S. agency securities are classified within Level 2. In addition, foreign government securities include a portion of the Emerging Market Debt (“EMD”) portfolio which is also classified within Level 2. Corporate. Corporate securities consist primarily of U.S. and foreign corporations covering a variety of industries and are for the most part priced by index providers and pricing vendors. Some issuers may participate in government programs which guarantee timely payment of principal and interest in the event of a default. The fair values of these securities are generally determined using the spread above the risk-free yield curve. Inputs used in the evaluation of these securities include credit data, interest rate data, market observations and sector news, broker-dealer quotes and trade volumes. In addition, corporate securities include a portion of the EMD portfolio. The Company classifies all of these securities within Level 2. Mortgage-backed Securities. The Company’s residential and commercial mortgage-backed securities consist of bonds issued by the Government National Mortgage Association, the FNMA and the FHLMC as well as private non-agency issuers. The fair values of these securities are determined through the use of a pricing model (including Option Adjusted Spread) which uses prepayment speeds and spreads to determine the appropriate average life of the mortgage-backed security. These spreads are generally obtained from broker-dealers, trade prices and the new issue market. As the significant inputs used to price mortgage-backed securities are observable market inputs, these securities are classified within Level 2. Asset-backed Securities. The underlying collateral for the Company’s asset-backed securities consists mainly of student loans, automobile loans and credit card receivables. These securities are primarily priced by index providers and pricing vendors. Inputs to the valuation process include broker-dealer quotes and other available trade information, prepayment speeds, interest rate data and credit spreads. The Company classifies these securities within Level 2. Short-term Investments. Short-term investments comprise highly liquid debt securities with a maturity greater than three months but less than one year from the date of purchase. Short-term investments are valued in a manner similar to the Company’s fixed income investments and are classified within Levels 1 and 2. Catastrophe Bonds. Catastrophe bonds held by the Company are variable rate fixed income instruments with redemption values adjusted based on the occurrence of a covered event, usually windstorms and earthquakes. These bonds have been classified as trading and carried at fair value. Bonds are priced using an average of multiple broker-dealer quotes and, as such, are classified as Level 2. Foreign Exchange Contracts. The foreign exchange contracts which the Company uses to mitigate currency risk are characterized as OTC due to their customized nature and the fact that they do not trade on a major exchange. These instruments trade globally in a deep, liquid market, providing substantial price transparency and accordingly are classified as Level 2. Interest Rate Swaps . The interest rate swaps which the Company uses to mitigate interest risk are characterized as OTC and are valued by the counterparty using quantitative models with multiple market inputs. The market inputs, such as interest rates and yield curves, are observable and the valuation can be compared for reasonableness with third-party pricing services. Consequently, these instruments are classified as Level 2. Other investments. The Company’s other investments represent our investment in a real estate fund. Adjustments to the fair value are made based on the net asset value of the investment. The net valuation criteria established by the manager of such investments are established in accordance with the governing documents and the asset manager’s valuation guidelines, which consider a two part approach: the discounted cash flows approach and the performance multiple approach, which uses a multiple/capitalization rate derived from market metrics from comparable companies or assets to produce operating performance metrics. Alternative valuation methodologies may be employed for investments with unusual characteristics. Loan Notes Issued by Silverton . Silverton, a licensed special purpose insurer, is consolidated into the Company’s accounts as a VIE. In the fourth quarter of 2014, Silverton issued an additional $85.0 million ( $70.0 million third-party funded) of Loan Notes with a maturity date of September 18, 2017. In the fourth quarter of 2015, Silverton issued an additional $125.0 million ( $100.0 million third-party funded) of Loan Notes with a maturity date of September 17, 2018. In the fourth quarter of 2016, Silverton issued an additional $130.0 million ( $105.0 million third-party funded) of Loan Notes with a maturity date of September 16, 2019. Silverton was not renewed in 2017 and has not issued any Loan Notes since, in the future, any such quota share support for Aspen Re will be provided by a separate cell of Peregrine. The Company elected to account for the Loan Notes at fair value using the guidance as prescribed under ASC 825, Financial Instruments as the Company believes it represents the most meaningful measurement basis for these liabilities. The Loan Notes are recorded at fair value at each reporting period and, as they are not quoted on an active market and contain significant unobservable inputs, they have been classified as a Level 3 instrument in the Company’s fair value hierarchy. The Loan Notes are unique because they are linked to the specific risks of the Company’s property catastrophe book. To determine the fair value of the Loan Notes the Company runs an internal model which considers the seasonality of the risk assumed under the retrocessional agreement between Aspen Bermuda or a combination of Aspen Bermuda and Aspen U.K., as ceding reinsurers, and Silverton. The seasonality used in the model is initially determined by applying the percentage of property catastrophe losses planned by the Company’s actuaries to the estimated written premium to determine earned premium for each quarter. The inputs to the internal model are based on Company specific data due to the lack of observable market inputs. Reserves for losses are the most significant unobservable input. An increase in reserves for losses would normally result in a decrease in the fair value of the Loan Notes while a decrease in reserves would normally result in an increase in the fair value of the Loan Notes. The observable and unobservable inputs used to determine the fair value of the Loan Notes as at March 31, 2019 and December 31, 2018 are presented in the tables below: As at March 31, 2019 Fair Value Level 3 Valuation Method Observable (O) and Unobservable (U) inputs Low High ($ in millions) ($ in millions) Loan Notes $ 5.9 (1) Internal Valuation Model Gross premiums written (O) $ 50.1 $ 61.1 Reserve for losses (U) $ 4.2 $ 61.9 Contract period (O) N/A 365 days Initial value of issuance (O) $ 325.0 $ 325.0 As at December 31, 2018 Fair Value Level 3 Valuation Method Observable (O) and Unobservable (U) inputs Low High ($ in millions) ($ in millions) Loan Notes $ 4.6 (1) Internal Valuation Model Gross premiums written (O) $ 50.1 $ 61.1 Reserve for losses (U) $ 4.2 $ 61.9 Contract period (O) N/A 365 days Initial value of issuance (O) $ 325.0 $ 325.0 (1) The amounts classified within accrued expenses and other payables were $5.9 million and $4.6 million as at March 31, 2019 and December 31, 2018 , respectively. The observable and unobservable inputs represent the potential variation around the inputs used in the internal model. The contract period is defined in the respective Loan Notes agreements and the initial value represents the funds received from third parties. For further information regarding Silverton, refer to Note 7 of these unaudited condensed consolidated financial statements.

Reinsurance

Reinsurance	3 Months Ended
	Mar. 31, 2019
Insurance [Abstract]
Reinsurance	Reinsurance The Company purchases retrocession and reinsurance to limit and diversify the Company’s risk exposure and increase its own reinsurance and insurance underwriting capacity. These agreements provide for recovery of a portion of losses and loss adjustment expenses from reinsurers. As is the case with most reinsurance contracts, the Company remains liable to the extent that reinsurers do not meet their obligations under these agreements and therefore, in line with its risk management objectives, the Company evaluates the financial condition of its reinsurers and monitors concentrations of credit risk. The total amount recoverable by the Company from reinsurers as at March 31, 2019 was $2,122.9 million ( December 31, 2018 — $2,077.6 million ) of which $1,642.0 million was uncollateralized ( December 31, 2018 — $1,497.8 million ). As at March 31, 2019 16.1% ( December 31, 2018 — 15.7% ) of the Company’s uncollateralized reinsurance recoverables were with Munich Re which is rated A+ by A.M Best and AA- by S&P, 9.5% ( December 31, 2018 — 10.2% ) with Lloyd’s Syndicates which are rated A by A.M Best and A+ by S&P and 10.0% ( December 31, 2018 — 10.2% ) with Everest Re which is rated A+ by A.M Best and A+ by S&P. These are the Company’s largest exposures to individual reinsurers. The Company has made no provision for doubtful debts from any of its reinsurers as at March 31, 2019 .

Derivative Contracts

Derivative Contracts	3 Months Ended
	Mar. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Contracts	Derivative Contracts The following tables summarize information on the location and amounts of derivative fair values on the consolidated balance sheet as at March 31, 2019 and December 31, 2018 : As at March 31, 2019 As at December 31, 2018 Derivatives Not Designated as Hedging Instruments Under ASC 815 Balance Sheet Location Notional Amount Fair Value Notional Amount Fair Value ($ in millions) ($ in millions) Foreign Exchange Contracts Derivatives at Fair Value $ 667.6 $ 8.9 $ 496.5 $ 14.6 Foreign Exchange Contracts Liabilities under Derivative Contracts $ 606.5 $ (7.2 ) (1) $ 760.8 $ (13.9 ) Interest Rate Swaps Liabilities under Derivative Contracts $ 3,318.0 $ (49.5 ) (2) $ — $ — (1) Net of $2.3 million cash collateral ( December 31, 2018 — $2.3 million ). (2) Initial and variation margin of $109.1 million has been posted ( December 31, 2018 — $ Nil ). As at March 31, 2019 As at December 31, 2018 Derivatives Designated as Hedging Instruments Under ASC 815 Balance Sheet Location Notional Amount Fair Value Notional Amount Fair Value ($ in millions) ($ in millions) Foreign Exchange Contracts Derivatives at Fair Value $ 70.8 $ 1.9 $ — $ — Foreign Exchange Contracts Liabilities under Derivative Contracts $ — $ — $ 94.3 $ (1.2 ) The following table provides the unrealized and realized gains recorded in the statements of operations and other comprehensive income for derivatives that are not designated or designated as hedging instruments under ASC 815 - “Derivatives and Hedging” for the three months ended March 31, 2019 and 2018 . Amount of Gain Recognized on Derivatives Three Months Ended Location of Gain Recognized on Derivatives March 31, 2019 March 31, 2018 Derivatives not designated as hedges ($ in millions) Foreign Exchange Contracts Change in Fair Value of Derivatives (3.1 ) 23.5 Interest Rate Swaps Change in Fair Value of Derivatives (50.2 ) — Derivatives designated as hedges Foreign Exchange Contracts General, administrative and corporate expenses 0.4 1.7 Foreign Exchange Contracts Net change from current period hedged transactions 1.7 0.9 Foreign Exchange Contracts. The Company uses foreign exchange contracts to manage foreign currency risk associated with our operating expenses but also foreign exchange risk associated with net assets or liabilities in currencies other than the U.S. dollar. A foreign exchange contract involves an obligation to purchase or sell a specified currency at a future date at a price set at the time of the contract. Foreign exchange contracts will not eliminate fluctuations in the value of the Company’s assets and liabilities denominated in foreign currencies but rather allow it to establish a rate of exchange for a future point in time. As at March 31, 2019 , the Company held foreign exchange contracts that were not designated as hedging under ASC 815 with an aggregate notional value of $1,274.1 million ( December 31, 2018 — $1,257.3 million ). The foreign exchange contracts are recorded as derivatives at fair value with changes recorded as a change in fair value of derivatives in the statement of operations. For the three months ended March 31, 2019 , the impact of foreign exchange contracts on net income was a loss of $3.1 million ( March 31, 2018 — gain of $23.5 million ). As at March 31, 2019 , the Company held foreign exchange contracts that were designated as hedging under ASC 815 with an aggregate nominal amount of $70.8 million ( December 31, 2018 — $94.3 million ). The foreign exchange contracts are recorded as derivatives at fair value in the balance sheet with the change in fair value recorded in other comprehensive income. The movement in other comprehensive income for the three months ended March 31, 2019 was a net unrealized gain of $1.7 million ( March 31, 2018 — gain of $0.9 million ). As the foreign exchange contracts settle, the realized gain or loss is reclassified from other comprehensive income into general, administration and corporate expenses of the statement of operations and other comprehensive income. For the three months ended March 31, 2019 , the amount recognized within general, administrative and corporate expenses for settled foreign exchange contracts was a realized gain of $0.4 million ( March 31, 2018 — gain of $1.7 million ). Interest Rate Swaps. During the three months ended March 31, 2019 , the Company entered into fixed for floating interest rate swaps with a total notional amount of $3,318.0 million due to mature between January 18, 2021 and January 18, 2034. The interest rate swaps are used in the ordinary course of the Company’s investments activities to partially mitigate the negative impact of rises in interest rates on the market value of the Company’s fixed income portfolio. For the three months ended March 31, 2019 , there was a loss of $50.2 million ( March 31, 2018 — gain of $ Nil ). As at March 31, 2019 , initial and variation margin with a fair value of $109.1 million was posted to a Futures Commission Merchant to support the current valuation of the interest rate swaps ( December 31, 2018 — $ Nil ). As at March 31, 2019 , no non-cash collateral was transferred to the Company by its counterparties ( December 31, 2018 — $ Nil ). Transfers of margin are recorded on the consolidated balance sheet within Derivatives at Fair Value, while transfers in respect of non-cash collateral are disclosed but not recorded. As at March 31, 2019 , no amount was recorded in the consolidated balance sheet for the pledged assets.

Deferred Policy Acquisition Cos

Deferred Policy Acquisition Costs	3 Months Ended
	Mar. 31, 2019
Insurance [Abstract]
Deferred Policy Acquisition Costs	Deferred Policy Acquisition Costs The following table represents a reconciliation of beginning and ending deferred policy acquisition costs for the three months ended March 31, 2019 and 2018 : Three Months Ended March 31, 2019 2018 ($ in millions) Balance at the beginning of the period $ 248.5 $ 294.3 Acquisition costs deferred 128.1 116.4 Amortization of deferred policy acquisition costs (88.2 ) (90.8 ) Balance at the end of the period $ 288.4 $ 319.9

Reserves for Losses and Loss Ad

Reserves for Losses and Loss Adjustment Expenses	3 Months Ended
	Mar. 31, 2019
Insurance [Abstract]
Reserves For Loss And Adjustment Expenses	Reserves for Losses and Loss Adjustment Expenses The following table represents a reconciliation of beginning and ending consolidated loss and loss adjustment expenses (“LAE”) reserves for the three months ended March 31, 2019 and 2018 and the twelve months ended December 31, 2018 : Three Months Ended March 31, 2019 Three Months Ended March 31, 2018 Twelve Months Ended December 31, 2018 ($ in millions) Provision for losses and LAE at the start of the year $ 7,074.2 $ 6,749.5 $ 6,749.5 Less reinsurance recoverable (2,077.6 ) (1,515.2 ) (1,515.2 ) Net loss and LAE at the start of the year 4,996.6 5,234.3 5,234.3 Provision for losses and LAE for claims incurred: Current year 304.2 347.9 1,684.1 Prior years 7.6 (37.7 ) (111.1 ) Total incurred 311.8 310.2 1,573.0 Losses and LAE payments for claims incurred: Current year (7.1 ) (7.4 ) (285.7 ) Prior years (474.8 ) (483.7 ) (1,441.0 ) Total paid (481.9 ) (491.1 ) (1,726.7 ) Foreign exchange losses/(gains) 50.9 14.7 (84.0 ) Net losses and LAE reserves at period end 4,877.4 5,068.1 4,996.6 Plus reinsurance recoverable on unpaid losses at period end 2,122.9 1,611.3 2,077.6 Provision for losses and LAE at the end of the relevant period $ 7,000.3 $ 6,679.4 $ 7,074.2 For the three months ended March 31, 2019 , there was an increase of $7.6 million in the Company’s estimate of the ultimate claims to be paid in respect of prior accident years compared to a reduction of $37.7 million for the three months ended March 31, 2018 . For additional information on the reserve releases, please refer to “Management’s Discussion and Analysis of Financial Condition and Results of Operations — Reserves for Losses and Loss Adjustment Expenses”.

Capital Structure

Capital Structure	3 Months Ended
	Mar. 31, 2019
Equity [Abstract]
Capital Structure	Capital Structure The following table provides a summary of the Company’s authorized and issued share capital as at March 31, 2019 and December 31, 2018 : As at March 31, 2019 As at December 31, 2018 Number $ in Thousands Number $ in Thousands Authorized share capital: Ordinary Shares $0.01 per share (2018: 0.15144558¢ per share) 70,000,000 700 969,629,030 1,469 Non-Voting Shares 0.15144558¢ per share — — 6,787,880 10 Preference Shares 0.15144558¢ per share 30,000,000 45 100,000,000 152 Total authorized share capital 745 1,631 Issued share capital: Issued ordinary shares of $0.01 per share (2018: 0.15144558¢ per share) 60,395,839 604 59,743,156 90 Issued 5.95% preference shares of 0.15144558¢ each with a liquidation preference of $25 per share 11,000,000 17 11,000,000 17 Issued 5.625% preference shares of 0.15144558¢ each with a liquidation preference of $25 per share 10,000,000 15 10,000,000 15 Total issued share capital 636 122 Additional paid-in capital as at March 31, 2019 was $967.8 million ( December 31, 2018 — $967.5 million ). Additional paid-in capital includes the aggregate liquidation preferences of the Company’s preference shares of $525.0 million ( December 31, 2018 — $525.0 million ) less issue costs of $13.1 million ( December 31, 2018 — $13.1 million ). Ordinary Shares. The following table summarizes transactions in the Company’s ordinary shares during the three months ended March 31, 2019 : Number of Ordinary Shares Ordinary shares of 0.015144558c per share Ordinary shares in issue as at December 31, 2018 59,743,156 Ordinary shares issued to employees under the 2013 share incentive plan and/or 2008 share purchase plan 144,269 Ordinary shares issued to non-employee directors 6,993 Ordinary shares canceled (59,894,418 ) Total ordinary shares of 0.015144558c per share in issue — Ordinary shares of $0.01 per share New ordinary shares issued of $0.01 per share 60,395,839 Ordinary shares in issue as at March 31, 2019 60,395,839 Authorized and Issued Ordinary Shares. The Company did not acquire any ordinary shares for the three months ended March 31, 2019 . Pursuant to the Merger Agreement, however, at the effective time of the Merger, each ordinary share of the Company issued and outstanding immediately prior to such time (other than ordinary shares owned by the Company as treasury shares, owned by any subsidiary of the Company or owned by Parent, Merger Sub or any subsidiary thereof) was automatically canceled and converted into the right to receive $42.75 in cash, without interest and less any required tax withholdings. The Company’s ordinary shares ceased trading on the New York Stock Exchange (the “NYSE”) prior to the opening of trading on February 15, 2019. Pursuant to the terms of the Merger Agreement, the memorandum of association and bye-laws of Merger Sub immediately prior to the effective time of the Merger became the memorandum of association and bye-laws, respectively, of the Company at the effective time of the Merger and will remain the memorandum of association (the “Altered Memorandum of Association”) and bye-laws, respectively, of the Company, until changed or amended as provided therein or pursuant to applicable law. The Company’s authorized share capital, as set out in the Altered Memorandum of Association, is $745,434 divided into 70,000,000 ordinary shares of par value $0.01 and 30,000,000 preference shares of par value 0.15144558¢ . Immediately prior to the effective time of the Merger, Parent held 60,395,839 of ordinary shares of Merger Sub, par value $0.01 . Pursuant to the terms of the Merger Agreement, each common share of Merger Sub issued and outstanding immediately prior to the effective time of the Merger was canceled and converted into and became one duly authorized, validly issued, fully paid and non-assessable ordinary share, par value of $0.01 , of the Company, as the surviving company. Preference Share Issuance. The Company did not issue any preference shares during the three months ended March 31, 2019 or March 31, 2018 .

Share-Based Payments

Share-Based Payments	3 Months Ended
	Mar. 31, 2019
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Payments	Share-Based Payments The Company had previously issued options and other equity incentives under the 2003 Share Incentive Plan, the 2013 Share Incentive Plan, the 2016 Stock Incentive Plan for Non-Employee Directors, the Amended 2006 Stock Option Plan, the 2008 Employee Share Purchase Plan and the Amended 2008 Sharesave Scheme. When options were exercised or other equity awards (excluding phantom shares) vested, new ordinary shares were issued as the Company did not hold treasury shares. Phantom shares were settled in cash in lieu of ordinary shares upon vesting. Immediately prior to the Merger, the Company took all actions necessary to enable and require existing participants in the ESPP to utilize their accumulated payroll deductions to purchase newly issued ordinary shares in accordance with the terms of the ESPP and, immediately after such purchases were completed, the Company terminated the ESPP. In accordance with the Merger Agreement, at the effective time of the Merger each issued and outstanding ordinary share of the Company (other than any ordinary shares that were owned by the Company as treasury shares, owned by any subsidiary of the Company or owned by Parent, Merger Sub or any subsidiary thereof) was automatically canceled and converted into the right to receive $42.75 in cash, without interest and less any required tax withholdings (the “Merger Consideration”). In addition, at the effective time of the Merger, all outstanding restricted share units and phantom shares, in each case, that were subject to performance-based vesting requirements, to the extent not vested, vested in full (with respect to any performance period that had been completed, determined based on actual level of performance achieved, and, with respect to any performance period that had not been completed, determined based on achievement of performance-based vesting requirements at target payout levels) and were cashed out based on the per share Merger Consideration. All other outstanding restricted share unit awards, to the extent not vested, vested in full and were cashed out based on the per share Merger Consideration plus a cash amount for any accrued but unpaid dividends in respect of such awards prior to the Effective Time. As a result, the total unrecognized share-based compensation expense related to the unvested awards was expensed and no share-based awards remain outstanding at March 31, 2019 . For the three months ended March 31, 2019 , the Company’s total share-based compensation expense was $21.6 million , which primarily related to the vesting of the share-based awards at the effective time of the Merger. Under the terms of the Merger Agreement, the settlement of these previously unvested share-based compensation awards totaling $21.6 million was funded by Parent.

Intangible Assets and Goodwill

Intangible Assets and Goodwill	3 Months Ended
	Mar. 31, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets and Goodwill	Intangible Assets and Goodwill The following tables provide a summary of the Company’s intangible assets for the three months ended March 31, 2019 and 2018 : Three Months Ended March 31, 2019 Three Months Ended March 31, 2018 Beginning of the Period Additions Amortization End of the Period Beginning of the Period Additions Amortization End of the Period ($ in millions) ($ in millions) Intangible Assets Trademarks $ 2.5 $ — $ (0.1 ) $ 2.4 $ 2.9 $ — $ (0.1 ) $ 2.8 Insurance Licenses 16.7 — — 16.7 16.7 — — 16.7 Agency Relationships 1.8 — (0.1 ) 1.7 2.3 — (0.1 ) 2.2 Non-compete Agreements 0.4 — (0.1 ) 0.3 0.7 — (0.1 ) 0.6 Goodwill 3.9 — — 3.9 3.9 — — 3.9 Renewal Rights 1.0 — (0.1 ) 0.9 1.4 — (0.1 ) 1.3 Total $ 26.3 $ — $ (0.4 ) $ 25.9 $ 27.9 $ — $ (0.4 ) $ 27.5 Crop Re and AgriLogic On December 18, 2017, Aspen U.S. Holdings sold its interest in AgriLogic to CGB Diversified Service, Inc (“CGB DS”) in exchange for a 23.2% equity interest in Crop Re Services LLC. Aspen U.S. Holdings retained the agricultural consulting business previously integrated within AgriLogic. Intangible assets disposed of as part of the AgriLogic sale included $21.8 million of agency relationships, $3.1 million for the right to use the AgriLogic trademark, $0.9 million of non-compete agreements and $20.6 million of goodwill. Following the sale the Company performed its annual qualitative assessment on the residual intangible assets of the agricultural consulting business and determined that it was more likely than not that the intangible assets were impaired. The Company therefore recognized an impairment charge of $3.4 million in the year ended December 31, 2017. On September 18, 2018, Aspen U.S. Holdings sold a 60% interest in AgriLogic Consulting, LLC, its agricultural consulting business, to CGB DS and an individual investor, recognizing no gain or loss on disposal and de-consolidation. Intangible assets of the consulting business had previously been fully impaired. Blue Waters On October 31, 2016, Acorn acquired 100% of the equity voting interest of Blue Waters, a specialist marine insurance agency. The total consideration for the acquisition was $8.0 million . A significant proportion of the acquired business was represented by intangible assets, specifically $3.1 million for agency relationships, $1.5 million for the right to use the Blue Waters trademark, $1.0 million for non-compete agreements and $0.05 million for the value of trading licenses. In addition, $0.3 million of residual net assets were acquired. The total net assets acquired of $5.75 million resulted in the Company recognizing a total of $2.1 million in goodwill for the acquisition of Blue Waters. Agency Relationships . The Company valued the agency relationships at $3.1 million with an estimated economic useful life of 5 years. The Company will amortize the estimated value of the agency relationships over their estimated useful life. License to use the “Blue Waters” Trademark . The Company acquired the right to use the Blue Waters trademark in the United States. The Company valued the trademark at $1.5 million with an estimated economic useful life of 5 years. The Company will amortize the estimated value of the trademark over its estimated useful life. Non-compete Agreements . The Company valued the non-compete agreements at $1.0 million with an estimated economic useful life of 5 years. The Company will amortize the estimated value of the non-compete agreements over their estimated useful life. Insurance Licenses . The Company valued the insurance licenses at $0.05 million . The insurance licenses are considered to have an indefinite useful life and are not amortized. The licenses are tested annually for impairment. Goodwill . The Company valued the goodwill at $2.1 million . The goodwill is deemed to have an indefinite useful life and is assessed for impairment annually. Other Intangible Assets Renewal Rights. On September 22, 2016, the Company entered into a renewal rights agreement with Liberty Specialty Markets Limited (“LSML”). The Company valued the renewal rights at $1.9 million with an estimated economic useful life of 5 years . The Company will amortize the estimated value of the renewal rights over the estimated useful life. In addition to the intangible assets and goodwill associated with the AgriLogic and Blue Waters acquisitions and the renewal rights agreement with LSML, the Company has the following intangible assets from prior transactions: License to use the “Aspen” Trademark. On April 5, 2005, the Company entered into an agreement with Aspen (Actuaries and Pension Consultants) Plc to acquire the right to use the Aspen trademark in the United Kingdom. The consideration paid was approximately $1.6 million . As at March 31, 2019 , the value of the license to use the Aspen trademark was $1.6 million ( December 31, 2018 — $1.6 million ). The trademark has an indefinite useful life and is tested for impairment annually or when events or changes in circumstances indicate that the asset might be impaired. Insurance Licenses. The total value of the Company’s licenses as at March 31, 2019 was $16.6 million ( December 31, 2018 — $16.6 million ). This includes $10.0 million of acquired licenses held by AAIC, $4.5 million of acquired licenses held by Aspen Specialty and $2.1 million of acquired licenses held by Aspen U.K. The insurance licenses are considered to have an indefinite life and are not amortized. The licenses are tested for impairment annually or when events or changes in circumstances indicate that the asset might be impaired. Goodwill. On January 1, 2017, the Company purchased through its wholly-owned subsidiary, Aspen U.S. Holdings, a 49% share of Digital Re. The Company valued the goodwill at $1.8 million . The goodwill is deemed to have an indefinite useful life and will be assessed for impairment annually.

Operating Leases

Operating Leases	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Lessee, Operating Leases	Operating Leases As at March 31, 2019, the Company has recognized Right-of-use operating lease assets of $91.4 million and operating lease liabilities of $93.9 million . Right-of-use operating lease assets comprise primarily of leased office real estate globally and other assets. For all office real estate leases, rent incentives, including reduced-rent and rent free periods and contractually agreed rent increases during the lease term, have been included when determining the present value of future cash flows. The Company believe that our office space is sufficient for us to conduct our operating for the foreseeable future in these locations. The Company has no lease transactions between related parties. Comparatives have not been presented due to 2019 being the first year of adoption of ASU 2016-2, “ Leases (Topic 842) ”. Operating lease charge. The following table summarizes the operating lease charge for the three months ended March 31, 2019 : For the Three Months Ended March 31, 2019 ($ in millions) Amortization charge on Right-of-use operating leased assets $ 3.3 Interest on operating lease liabilities $ 1.2 Operating lease charge $ 4.5 Lease Liabilities. The following table summarizes the maturity of lease liabilities under non-cancellable leases as of March 31, 2019 : March 31, 2019 ($ in millions) Operating leases - maturities 2019 $ 12.9 2020 $ 14.2 2021 $ 11.8 2022 $ 9.4 2023 $ 8.9 Later years $ 64.5 Total minimum lease payments $ 121.7 Less imputed interest $ (27.8 ) Total lease liabilities $ 93.9 Other lease information. The following table summarizes the cash flows on operating leases for the three months ended March 31, 2019 and other supplemental information: For the Three Months Ended March 31, 2019 ($ in millions) Cash paid for amounts included in the measurement of lease liabilities - Operating cash outflow from operating leases $ (4.5 ) Right-of-use assets obtained in exchange for lease obligations - Operating leases $ 3.1 Reduction to Right-of-use assets resulting from reductions to lease obligations - Operating leases $ 1.2 Weighted Averages - Operating leases, remaining lease terms (years) 10.5 - Operating leases, average discount rate 5.0 %

Commitments and Contingent Liab

Commitments and Contingent Liabilities	3 Months Ended
	Mar. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingent Liabilities	Commitments and Contingent Liabilities (a) Restricted assets The Company is obliged by the terms of its contractual obligations to specific policyholders and by obligations to certain regulatory authorities to facilitate issue of letters of credit or maintain certain balances in deposits and trust funds for the benefit of policyholders. The following table details the forms and value of the Company’s restricted assets as at March 31, 2019 and December 31, 2018 : As at March 31, 2019 As at December 31, 2018 ($ in millions, except percentages) Regulatory trusts and deposits: Affiliated transactions $ 922.5 $ 1,033.9 Third party 2,745.7 2,511.7 Letters of credit / guarantees (1) 792.4 771.1 Investment commitment — real estate fund — — Other investments — real estate fund 104.0 102.5 Total restricted assets $ 4,564.6 $ 4,419.2 Total as percent of investable assets (2) 58.5 % 56.4 % (1) As at March 31, 2019 , the Company had pledged funds in the amount of $792.4 million ( December 31, 2018 — $771.1 million ) as collateral for the secured letters of credit. (2) Investable assets comprise total investments, cash and cash equivalents, accrued interest, receivables for securities sold and payables for securities purchased. Real Estate Fund. On December 20, 2017, the Company committed $100.0 million as a limited partner to a real estate fund. The investment objective of the fund is to achieve attractive risk-adjusted returns through the acquisition of income producing, high quality assets in gateway cities located in the U.S. and Canada in the office, retail, industrial and multifamily sectors of the real estate market. On May 1, 2018, the Company received a demand for an initial capital call of $86.2 million and paid the capital call on May 10, 2018. On September 19, 2018, the Company received a demand for the final capital call of $13.8 million and paid the capital on September 28, 2018. Investments in this real estate fund may be redeemed on a quarterly basis with 90 days’ notice subject to available cash in the fund once the lock-up period ends two years after the capital call. If sufficient cash is not available then all requested redemptions will be made on a pro rata basis. If a redemption request has not been met in full, as of such calendar quarter, the remaining portion of the request will be redeemed in subsequent quarters. There are no assurances as to when the Company may be able to withdraw, in whole or in part, its redemption request from the fund. A lock-up period is the initial amount of time an investor is contractually required to remain invested before having the ability to redeem. Funds at Lloyd’s. AUL operates at Lloyd’s as the corporate member for Syndicate 4711. Lloyd’s determines Syndicate 4711’s required regulatory capital principally through the syndicate’s annual business plan. Such capital, called Funds at Lloyd’s, consists of investable assets as at March 31, 2019 in the amount of $516.2 million ( December 31, 2018 — $503.2 million ). The amounts provided as Funds at Lloyd’s are drawn upon and become a liability of the Company in the event Syndicate 4711 declares a loss at a level that cannot be funded from other resources, or if Syndicate 4711 requires funds to cover a short term liquidity gap. The amount which the Company provides as Funds at Lloyd’s is not available for distribution to the Company for the payment of dividends. Aspen Managing Agency Limited, the managing agent to Syndicate 4711, is also required by Lloyd’s to maintain a minimum level of capital which as at March 31, 2019 was £0.4 million ( December 31, 2018 — £0.4 million ). This is not available for distribution by the Company for the payment of dividends. Credit Agreement. On March 27, 2017, Aspen Holdings and certain of its direct or indirect subsidiaries (collectively, the “Borrowers”) entered into a Second Amended and Restated Credit Agreement (the “Credit Agreement”) with various lenders and Barclays Bank plc, as administrative agent. The Credit Agreement will be used by the Borrowers to finance the working capital needs of the Company and its subsidiaries, for letters of credit in connection with the insurance and reinsurance businesses of the Company and its subsidiaries and for other general corporate purposes. Initial availability under the Credit Agreement is $200 million and the Company has the option (subject to obtaining commitments from acceptable lenders) to increase the Credit Agreement by up to $100 million . The Credit Agreement will expire on March 27, 2022. As at March 31, 2019 , no borrowings were outstanding under the Credit Agreement. The fees and interest rates on the loans and the fees on the letters of credit payable by the Borrowers under the Credit Agreement are based upon the credit ratings for the Company’s long-term unsecured senior debt by S&P and Moody’s. In addition, the fees for a letter of credit vary based upon whether the applicable Borrower has provided collateral (in the form of cash or qualifying debt securities) to secure its reimbursement obligations with respect to such letter of credit. Under the Credit Agreement, the Company must not permit (a) consolidated tangible net worth to be less than approximately $2,323,100,000 plus 25% of consolidated net income plus 25% of aggregate net cash proceeds from the issuance by the Company of its capital stock, in each case after January 1, 2017, (b) the ratio of its total consolidated debt to the sum of such debt plus its consolidated tangible net worth to exceed 35% or (c) any material insurance subsidiary to have a financial strength rating of less than B++ from A.M. Best. The Credit Agreement contains other customary affirmative and negative covenants, including (subject to various exceptions) restrictions on the ability of the Company and its subsidiaries to incur indebtedness, create or permit liens on their assets, engage in mergers or consolidations, dispose of assets, pay dividends or other distributions, purchase or redeem the Company’s equity securities, make investments and enter into transactions with affiliates. In addition, the Credit Agreement has customary events of default, including (subject to certain materiality thresholds and grace periods) payment default, failure to comply with covenants, material inaccuracy of representation or warranty, bankruptcy or insolvency proceedings, change of control and cross-default to other debt agreements. On August 28, 2018, the Borrowers entered into a Waiver to Credit Agreement with various lenders and Barclays Bank plc, as administrative agent, under which the lenders thereunder waived any Default or Event of Default (as each term is defined in the Credit Agreement) that would result from any Change of Control (as such term is defined in the Credit Agreement) caused by the Merger. Other Credit Facilities. On June 29, 2018, Aspen Bermuda and Citibank Europe plc (“Citi Europe”) amended the committed letter of credit facility, dated June 30, 2012, as amended on June 30, 2014 and June 30, 2016, (the “LOC Facility”). The amendment to the LOC facility extends the term of the LOC Facility to June 30, 2020 and provides a maximum aggregate amount of up to $550.0 million . Under the LOC Facility, Aspen Bermuda will pay to Citi Europe (a) a letter of credit fee based on the available amounts of each letter of credit and (b) a commitment fee, which varies based upon usage, on the unutilized portion of the LOC Facility. Aspen Bermuda will also pay interest on the amount drawn by any beneficiary under the LOC Facility at a rate per annum of LIBOR plus 1% (plus reserve asset costs, if any) from the date of drawing until the date of reimbursement by Aspen Bermuda. In addition, Aspen Bermuda and Citi Europe entered into an uncommitted letter of credit facility whereby Aspen Bermuda has the ability to request letters of credit under this facility subject to the prior approval of Citi Europe. The fee associated with the uncommitted facility is a letter of credit fee based on the available amounts of each letter of credit issued under the uncommitted facility. Both the LOC Facility and the uncommitted facility are used to secure obligations of Aspen Bermuda to its policyholders. In addition to these facilities, we also use regulatory trusts to secure our obligations to policyholders. The terms of a pledge agreement between Aspen Bermuda and Citi Europe (pursuant to an assignment agreement dated October 11, 2006) dated January 17, 2006, as amended, were also amended on June 30, 2014 to change the types of securities or other assets that are acceptable as collateral under the New LOC Facility. All other agreements relating to Aspen Bermuda’s LOC Facility, which now apply to the LOC Facility with Citi Europe, as previously filed with the SEC, remain in full force and effect. As at March 31, 2019 , we had $466.4 million of outstanding collateralized letters of credit under the LOC Facility ( December 31, 2018 — $444.2 million under the LOC Facility). On February 11, 2019, Aspen Holdings (acting as guarantor of Aspen European Holdings Limited (“Aspen European”)) and Aspen European entered into a letter of credit facility agreement with National Australia Bank Limited, London Branch, for the purpose of obtaining a letter of credit in favor of Aspen U.K. for a sum not to exceed $100 million . In the event Aspen U.K. demands payment of cash funds under this facility, Aspen Holdings as guarantor would be required to repay the letter of credit. A letter of credit was issued in favor of Aspen U.K. for a sum of $100 million which expires on February 11, 2023. (b) Contingent liabilities In common with the rest of the insurance and reinsurance industry, the Company is subject to litigation and arbitration in the ordinary course of business. The Company’s Operating Subsidiaries are regularly engaged in the investigation, conduct and defense of disputes, or potential disputes, resulting from questions of insurance or reinsurance coverage or claims activities. Pursuant to insurance and reinsurance arrangements, many of these disputes are resolved by arbitration or other forms of alternative dispute resolution. Such legal proceedings are considered in connection with estimating the Company’s Insurance Reserves — Loss and Loss Adjustment Expenses, as provided on the Company’s consolidated balance sheet. In some jurisdictions, noticeably the U.S., a failure to deal with such disputes or potential disputes in an appropriate manner could result in an award of “bad faith” punitive damages against the Company’s Operating Subsidiaries. In accordance with ASC 450-20-50-4b, for (a) reasonably possible losses for which no accrual is made because any of the conditions for accrual in ASC 450-20-25-2 are not met and (b) reasonably possible losses in excess of the amounts accrued pursuant to ASC 450-20-30-1, the Company will provide an estimate of the possible loss or range of possible loss or state that such an estimate cannot be made. As at March 31, 2019 and December 31, 2018 , based on available information, it was the opinion of the Company’s management that the probability of the ultimate resolution of pending or threatened litigation or arbitrations having a material effect on the Company’s financial condition, results of operations or liquidity would be remote.

Related Party Transactions

Related Party Transactions	3 Months Ended
	Mar. 31, 2019
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions In the normal course of the Company’s underwriting activities, the Company has entered into insurance and reinsurance agreements with companies affiliated with the Company. As noted above, Parent, an affiliate of certain investment funds managed by affiliates of Apollo, owns all of the Company’s ordinary shares. Additionally, certain employees of Apollo and its affiliates serve on the Board. As previously disclosed, the Company entered into a Management Consulting Agreement, dated March 28, 2019 (the “Management Consulting Agreement”), with Apollo Management Holdings, L.P. (“AMH”). Pursuant to the Management Consulting Agreement, AMH will provide the Company and its subsidiaries with management consulting and advisory services related to the business and affairs of the Company and its subsidiaries and the Company will pay to AMH in consideration for its services under the Management Consulting Agreement an annual management consulting fee equal to the greater of (i) 1% of the consolidated net income of the Company and its subsidiaries for the applicable fiscal year, and (ii) $5 million . The Management Consulting Agreement is effective February 15, 2019 (the “Commencement Date”) and has an initial term of eight years from the Commencement Date. The Management Consulting Agreement will be automatically extended for an additional 12 -month term on each of the eight -year and nine -year anniversary of the Commencement Date absent contrary notice by either party given not less than 30 days prior to such anniversary date. The Management Consulting Agreement will be automatically terminated on the occurrence of the consummation of any transaction or series of transactions, whether or not related, as a result of which New Holders (as defined in the Management Consulting Agreement) become the beneficial owner, directly or indirectly, of more than ninety percent of the ordinary shares or other common equity and voting securities of the Company and its subsidiaries.

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2019
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events On April 5, 2019, the Company decided not to establish a new insurance subsidiary in Dublin, Ireland to service the needs of its insurance customers in the European Economic Area post-Brexit and therefore withdrew its application to the Central Bank of Ireland to establish a new insurance subsidiary in Dublin as previously announced. The Company intends to service customer needs through Lloyd’s of London’s Brussels Subsidiary and the Company’s other bespoke arrangements. Depending on political agreements as part of Brexit negotiations regarding Solvency II equivalence for the United Kingdom, the Company believes that its insurance business will be largely unaffected by Brexit. In April 2019, following the completion of the Merger, Apollo Asset Management Europe PC LLP (“AAME”) was engaged as the investment manager for certain of our subsidiaries in Bermuda and the U.S. to provide centralized asset management investment advisory and risk services for the portfolio of investments of such subsidiaries pursuant to the investment management agreements (“IMAs”) that have been entered into with AAME. AAME is registered in England and Wales and is authorized and regulated by the Financial Conduct Authority in the United Kingdom under the Financial Services and Markets Act 2000 and the rules promulgated thereunder for the primary purpose of providing a centralized asset management and risk function to European clients in the financial services and insurance sectors. Pursuant to the IMAs, AAME may engage sub-advisors or delegates to provide certain of the investment advisory and management services to our subsidiaries. In this regard, AAME is able to leverage its relationships with other Apollo-affiliated investment advisors in a sub-advisory capacity, pursuant to which AAME has mandated its affiliates, Apollo Management International LLP (“AMI”) and Apollo Capital Management L.P. (“AMC”), to invest in asset classes in which they have investment expertise and sourcing capabilities, such as middle market loans, commercial mortgage loans, structured products and short term secured investments. Under each of the IMAs, AAME will be paid an annual investment management fee (the “Management Fee”) which will be based on a cost-plus structure. The “cost” is comprised of the direct and indirect fees, costs, expenses and other liabilities arising in or otherwise connected with the services provided under the IMAs. The “plus” component will be a mark-up in an amount of up to 25% determined based on an applicable transfer pricing study. The Management Fee will be subject to certain maximum threshold levels, including an annual fee cap of 15 bps of the total amount of investable assets. Affiliated sub-advisors, including AMI and AMC, will also earn additional fees for sub-advisory services rendered. For a more detailed description of these arrangements, refer to Item 13 “Certain Relationships and Related Transactions, and Director Independence” included in the Company’s Amended Annual Report on Form 10-K for the year ended December 31, 2018 filed with the SEC. See “Risk Factors” and “Cautionary Statement Regarding Forward-Looking Statements” included in this report.

Basis of Preparation (Policies)

Basis of Preparation (Policies)	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
New Accounting Pronouncements Adopted in 2019 and Not Yet Adopted	Accounting Pronouncements Adopted in 2019 On February 25, 2016, the Financial Accounting Standards Board (“FASB”) issued ASU 2016-2, “ Leases (Topic 842) ” which supersedes the leases requirements in Topic 840 and establishes the principles that lessees and lessors shall apply to report useful information to users of financial statements about the amount, timing, and uncertainty of cash flows arising from a lease. On July 30, 2018, the FASB issued ASU 2018-11, “ Targeted Improvements (Topic 842)” which amended the transitional guidance of ASU 2016-2, “ Leases (Topic 842)” and provided an alternative transition method to the existing modified retrospective method. In particular, the amendment allows entities to initially apply the new lease standard as at the adoption date and recognize a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. ASU 2018-11 was effective for fiscal years beginning after December 15, 2018, aligned to the effective date and transition requirements of ASU 2016-2. Following the adoption of ASU 2016-02 and ASU 2018-11, the Company recognized right-of-use operating leased assets of $91.2 million , consisting of leased office real estate and motor vehicles, and an operating lease liability of $93.6 million on the balance sheet as of January 1, 2019, and a cumulative effect adjustment of $2.4 million through opening retained earnings. The interest rate assumption applied in determining the present value of future cash flows of 5% was determined based on the Company’s weighted average incremental borrowing rate. During the quarter ended March 31, 2019, additional right-of-use operating leased assets and a corresponding operating lease liability of $3.1 million have been recognized on balance sheet for new or renewed lease agreements. An operating lease charge of $4.5 million was incurred during the quarter, consisting of an amortization charge of $3.3 million on right-of-use operating leases assets and a $1.2 million finance charge on the operating lease liability. On March 5, 2019, the FASB issued ASU 2019-01, “ Codification Improvements (Topic 842)” which amended lessor accounting guidance in ASC 842 and clarifies exemption from certain interim period transitional disclosure requirements. The amendments of this ASU are effective for fiscal years beginning after December 15, 2018. Adoption of this ASU did not have a material impact on the Company’s financial statements and disclosures. On August 28, 2017, the FASB issued ASU 2017-12, “Derivatives and Hedging (Topic 815)” enabling entities to better align their hedge accounting and risk management activities, while also simplifying the application of hedge accounting in certain situations. This ASU is effective for fiscal years beginning after 15 December, 2018 using a modified retrospective approach for cash flow and net investment hedge relationships that exist on the date of adoption. Adoption of this ASU did not have a material impact on the Company’s financial statements and disclosures. On February 14, 2018, the FASB issued ASU 2018-02, “ Income Statement - Reporting Comprehensive Income (Topic 220)” which allows a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act. This ASU is effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years. Adoption of this ASU did not have a material impact on the Company's financial statements and disclosures. On June 20, 2018, the FASB issued ASU 2018-07, “ Compensation - Stock Compensation (Topic 718)” which amends the scope of Topic 718 via improvements to non-employee share-based payment accounting. Amendments include allowing companies to account for share-based payment transactions with non-employees in the same way as share-based payment transactions with employees and includes elections that offer relief to non-public companies when measuring non-employee equity share options. This ASU is effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years. Adoption of this ASU did not have a material impact on the Company's financial statements and disclosures. 2019 Accounting Pronouncements Not Yet Adopted Other accounting pronouncements issued during the three months ended March 31, 2019 were either not relevant to the Company or did not impact the Company’s consolidated financial statements.

Reclassifications from Accumu_2

Reclassifications from Accumulated Other Comprehensive Income (Tables)	3 Months Ended
	Mar. 31, 2019
Equity [Abstract]
Schedule of Accumulated Other Comprehensive Income Reclassification	The following tables set out the components of the Company’s accumulated other comprehensive income (“AOCI”) that are reclassified into the unaudited condensed consolidated statement of operations for the three months ended March 31, 2019 and 2018 : Amount Reclassified from AOCI Details about the AOCI Components Three Months Ended March 31, 2019 Three Months Ended March 31, 2018 Affected Line Item in the Unaudited ($ in millions) Available for sale securities: Realized gains on sale of securities $ 3.0 $ 2.0 Realized and unrealized investment gains Realized (losses) on sale of securities (3.2 ) (1.9 ) Realized and unrealized investment losses (0.2 ) 0.1 Income from operations before income tax Tax on net realized (losses) on securities — (0.1 ) Income tax benefit/(expense) $ (0.2 ) $ — Net income Realized derivatives: Net realized gains on settled derivatives $ 0.4 $ 1.7 General, administrative and corporate expenses Tax on settled derivatives (0.1 ) (0.3 ) Income tax benefit/(expense) $ 0.3 $ 1.4 Net income Total reclassifications from AOCI to the statement of operations, net of income tax $ 0.1 $ 1.4 Net income

Dividends (Tables)

Dividends (Tables)	3 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
Summary of Declared Dividends	Dividends. On May 1, 2019, the Company’s Board of Directors (the “Board of Directors”) declared the following quarterly dividends: Dividend Payable on: Record Date: 5.95% preference shares $ 0.3719 July 1, 2019 June 15, 2019 5.625% preference shares $ 0.3516 July 1, 2019 June 15, 2019

Segment Reporting (Tables)

Segment Reporting (Tables)	3 Months Ended
	Mar. 31, 2019
Segment Reporting [Abstract]
Summary of Gross and Net Written and Earned Premiums, Underwriting Results, Ratios and Reserves for Each of Company's Business Segments	The following tables provide a summary of gross and net written and earned premiums, underwriting results, ratios and reserves for each of the Company’s business segments for the three months ended March 31, 2019 and 2018 : Three Months Ended March 31, 2019 Reinsurance Insurance Total ($ in millions) Underwriting Revenues Gross written premiums $ 538.4 $ 475.4 $ 1,013.8 Net written premiums 395.6 222.0 617.6 Gross earned premiums 336.5 480.5 817.0 Net earned premiums 276.9 233.7 510.6 Underwriting Expenses Losses and loss adjustment expenses 165.8 146.0 311.8 Amortization of deferred policy acquisition costs 62.6 25.6 88.2 General and administrative expenses 27.2 59.0 86.2 Underwriting income $ 21.3 $ 3.1 24.4 Corporate expenses (11.9 ) Non-operating expenses (1) (39.2 ) Net investment income 51.5 Realized and unrealized investment gains 42.0 Realized and unrealized investment losses (6.2 ) Change in fair value of loan notes issued by variable interest entities (1.5 ) Change in fair value of derivatives (53.3 ) Interest expense on long term debt (5.5 ) Net realized and unrealized foreign exchange gains 5.1 Other income 1.7 Other expenses (0.9 ) Income before tax $ 6.2 Net reserves for loss and loss adjustment expenses $ 2,871.5 $ 2,005.9 $ 4,877.4 Ratios Loss ratio 59.9 % 62.5 % 61.1 % Policy acquisition expense ratio 22.6 11.0 17.3 General and administrative expense ratio 9.8 25.2 26.9 (2) Expense ratio 32.4 36.2 44.2 Combined ratio 92.3 % 98.7 % 105.3 % (1) Non-operating expenses includes $6.1 million of expenses related to the Company’s operating effectiveness and efficiency program (the “Effectiveness and Efficiency Program”) and $29.8 million of fees related to or triggered by the Merger. (2) The general and administrative expense ratio in the “Total” column includes corporate and non-operating expenses. Three Months Ended March 31, 2018 Reinsurance Insurance Total ( $ in millions) Underwriting Revenues Gross written premiums $ 623.5 $ 493.3 $ 1,116.8 Net written premiums 425.0 210.5 635.5 Gross earned premiums 375.0 467.6 842.6 Net earned premiums 282.5 251.0 533.5 Underwriting Expenses Losses and loss adjustment expenses 166.9 143.3 310.2 Amortization of deferred policy acquisition costs 55.9 34.9 90.8 General and administrative expenses 31.6 63.6 95.2 Underwriting income $ 28.1 $ 9.2 37.3 Corporate expenses (13.7 ) Non-operating expenses (1) (12.1 ) Net investment income 47.3 Realized and unrealized investment gains 100.6 Realized and unrealized investment losses (138.3 ) Change in fair value of loan notes issued by variable interest entities 1.0 Change in fair value of derivatives 23.5 Interest expense on long term debt (7.4 ) Net realized and unrealized foreign exchange (losses) (4.7 ) Other income 2.1 Other expenses (1.2 ) Income before tax $ 34.4 Net reserves for loss and loss adjustment expenses $ 2,823.6 $ 2,244.5 $ 5,068.1 Ratios Loss ratio 59.1 % 57.1 % 58.1 % Policy acquisition expense ratio 19.8 13.9 17.0 General and administrative expense ratio 11.2 25.3 22.7 (2) Expense ratio 31.0 39.2 39.7 Combined ratio 90.1 % 96.3 % 97.8 % (1) Non-operating expenses includes $11.8 million of expenses related to the Company’s Effectiveness and Efficiency Program. (2) The general and administrative expense ratio in the “Total” column includes corporate and non-operating expenses.

Investments (Tables)

Investments (Tables)	3 Months Ended
	Mar. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Summary of Investment Income	Investment Income. The following table summarizes investment income for the three months ended March 31, 2019 and 2018 : For the Three Months Ended March 31, 2019 March 31, 2018 ($ in millions) Fixed income securities — Available for sale $ 34.3 $ 33.3 Fixed income securities — Trading 11.7 12.0 Short-term investments — Available for sale 0.8 0.2 Short-term investments — Trading 0.2 0.2 Fixed term deposits (included in cash and cash equivalents) 4.5 2.4 Equity securities — Trading — 1.2 Catastrophe bonds — Trading 0.8 0.6 Other investments, at fair value 1.4 — Total $ 53.7 $ 49.9 Investment expenses (2.2 ) (2.6 ) Net investment income $ 51.5 $ 47.3
Net Realized and Unrealized Investment Gains and Losses and Change in Unrealized Gains and Losses on Investments	The following table summarizes the net realized and unrealized investment gains and losses recorded in the statement of operations and the change in unrealized gains and losses on investments recorded in other comprehensive income for the three months ended March 31, 2019 and 2018 : For the Three Months Ended March 31, 2019 March 31, 2018 ($ in millions) Available for sale: Fixed income securities — gross realized gains $ 3.0 $ 1.8 Fixed income securities — gross realized (losses) (3.2 ) (1.8 ) Cash and cash equivalents — gross realized gains — 0.2 Cash and cash equivalents — gross realized (losses) — (0.1 ) Trading: Fixed income securities — gross realized gains 2.3 1.6 Fixed income securities — gross realized (losses) (2.8 ) (7.0 ) Short-term investments — gross realized (losses) (0.1 ) — Cash and cash equivalents — gross realized gains 0.1 1.6 Equity securities — gross realized gains — 94.5 Equity securities — gross realized (losses) — (20.3 ) Catastrophe bonds — net unrealized gains 0.3 0.9 Net change in gross unrealized gains/(losses) 36.3 (108.8 ) Investments — equity method: Gross realized and unrealized (loss) in MVI — (0.1 ) Gross realized and unrealized (loss) in Bene (0.1 ) (0.2 ) Total net realized and unrealized investment gains/(losses) recorded in the statement of operations $ 35.8 $ (37.7 ) Change in available for sale net unrealized gains/(losses): Fixed income securities 75.6 (82.9 ) Change in taxes (5.2 ) 5.5 Total change in net unrealized gains/(losses), net of taxes, recorded in other comprehensive income $ 70.4 $ (77.4 )
Cost, Gross Unrealized Gains and Losses, and Estimated Fair Value of Available for Sale Investments in Fixed Income Maturities, Short-Term Investments and Equities	Fixed Income Securities and Short-Term Investments — Available For Sale. The following tables present the cost or amortized cost, gross unrealized gains and losses and estimated fair market value of available for sale investments in fixed income securities and short-term investments as at March 31, 2019 and December 31, 2018 : As at March 31, 2019 Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Market Value ($ in millions) U.S. government $ 1,352.6 $ 14.6 $ (8.0 ) $ 1,359.2 U.S. agency 39.3 0.3 (0.1 ) 39.5 Municipal 46.5 1.9 (0.2 ) 48.2 Corporate 2,151.6 21.8 (10.8 ) 2,162.6 Non-U.S. government-backed corporate 98.1 0.4 (0.2 ) 98.3 Non-U.S. government 356.9 4.9 (0.2 ) 361.6 Asset-backed 16.2 — (0.1 ) 16.1 Agency mortgage-backed 955.3 9.9 (10.2 ) 955.0 Total fixed income securities — Available for sale 5,016.5 53.8 (29.8 ) 5,040.5 Total short-term investments — Available for sale 160.7 0.2 — 160.9 Total $ 5,177.2 $ 54.0 $ (29.8 ) $ 5,201.4 As at December 31, 2018 Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Market Value ($ in millions) U.S. government $ 1,413.5 $ 6.8 $ (16.1 ) $ 1,404.2 U.S. agency 47.7 0.1 (0.4 ) 47.4 Municipal 46.7 1.3 (0.8 ) 47.2 Corporate 2,238.9 7.8 (40.5 ) 2,206.2 Non-U.S. government-backed corporate 93.2 0.2 (0.2 ) 93.2 Non-U.S. government 399.8 3.6 (0.8 ) 402.6 Asset-backed 17.4 — (0.1 ) 17.3 Agency mortgage-backed 1,025.1 6.5 (19.0 ) 1,012.6 Total fixed income securities — Available for sale 5,282.3 26.3 (77.9 ) 5,230.7 Total short-term investments — Available for sale 105.6 — — 105.6 Total $ 5,387.9 $ 26.3 $ (77.9 ) $ 5,336.3
Cost, Gross Unrealized Gains and Losses, and Estimated Fair Value of Trading Investments in Fixed Income Maturities	Fixed Income Securities, Short-Term Investments, Equities and Catastrophe Bonds — Trading. The following tables present the cost or amortized cost, gross unrealized gains and losses, and estimated fair market value of trading investments in fixed income securities, short-term investments, equity securities and catastrophe bonds as at March 31, 2019 and December 31, 2018 : As at March 31, 2019 Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Market Value ($ in millions) U.S. government $ 217.4 $ 1.6 $ (0.2 ) $ 218.8 Municipal 3.0 — — 3.0 Corporate 754.9 12.4 (3.4 ) 763.9 Non-U.S. government 246.4 6.8 (0.7 ) 252.5 Asset-backed 2.3 — — 2.3 Agency mortgage-backed 49.1 0.3 (0.6 ) 48.8 Total fixed income securities — Trading 1,273.1 21.1 (4.9 ) 1,289.3 Total short-term investments — Trading 81.0 — — 81.0 Total catastrophe bonds — Trading 39.5 — (1.4 ) 38.1 Total $ 1,393.6 $ 21.1 $ (6.3 ) $ 1,408.4 As at December 31, 2018 Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Market Value ($ in millions) U.S. government $ 146.6 $ 1.6 $ (0.5 ) $ 147.7 Municipal 2.8 — (0.1 ) 2.7 Corporate 734.2 2.6 (16.6 ) 720.2 Non-U.S. government 268.7 1.9 (5.2 ) 265.4 Asset-backed 2.4 — — 2.4 Agency mortgage-backed 50.3 0.2 (1.1 ) 49.4 Total fixed income securities — Trading 1,205.0 6.3 (23.5 ) 1,187.8 Total short-term investments — Trading 9.5 — — 9.5 Total catastrophe bonds — Trading 37.9 0.1 (1.8 ) 36.2 Total $ 1,252.4 $ 6.4 $ (25.3 ) $ 1,233.5
Other Investments	The table below shows the Company’s investments in the MVI, Bene, Digital Re and Crop Re for the three months ended March 31, 2019 : For the Three Months Ended March 31, 2019 MVI Bene Digital Re Crop Re Total ($ in millions) Opening undistributed value of investment $ 0.5 $ 3.2 $ 0.9 $ 62.5 $ 67.1 Investment in the period — — — — — Realized/unrealized losses for the three months to March 31, 2019 — (0.1 ) — — (0.1 ) Closing undistributed value of investment $ 0.5 $ 3.1 $ 0.9 $ 62.5 $ 67.0
Summary of Fixed Maturities	Fixed Income Securities. The scheduled maturity distribution of available for sale fixed income securities as at March 31, 2019 and December 31, 2018 is set forth in the tables below. Actual maturities may differ from contractual maturities because issuers of securities may have the right to call or prepay obligations with or without call or prepayment penalties. As at March 31, 2019 Amortized Cost or Cost Fair Market Value Average S&P Ratings by Maturity ($ in millions) Due one year or less $ 441.1 $ 440.7 AA- Due after one year through five years 2,463.8 2,467.0 AA- Due after five years through ten years 1,014.7 1,025.1 AA- Due after ten years 125.4 136.6 AA- Subtotal 4,045.0 4,069.4 Agency mortgage-backed 955.3 955.0 AA+ Asset-backed 16.2 16.1 AAA Total fixed income securities — Available for sale $ 5,016.5 $ 5,040.5 As at December 31, 2018 Amortized Cost or Cost Fair Market Value Average S&P Ratings by Maturity ($ in millions) Due one year or less $ 464.3 $ 463.5 AA- Due after one year through five years 2,605.7 2,582.0 AA- Due after five years through ten years 1,047.9 1,028.3 AA- Due after ten years 121.9 127.0 AA- Subtotal 4,239.8 4,200.8 Agency mortgage-backed 1,025.1 1,012.6 AA+ Asset-backed 17.4 17.3 AAA Total fixed income securities — Available for sale $ 5,282.3 $ 5,230.7
Aggregate Fair Value and Gross Unrealized Loss by Type of Security	Gross Unrealized Loss. The following tables summarize, by type of security, the aggregate fair value and gross unrealized loss by length of time the security has been in an unrealized loss position in the Company’s available for sale portfolio as at March 31, 2019 and December 31, 2018 : As at March 31, 2019 0-12 months Over 12 months Total Fair Market Value Gross Unrealized Loss Fair Market Value Gross Unrealized Loss Fair Market Value Gross Unrealized Loss Number of Securities ($ in millions) U.S. government $ 90.9 $ (0.2 ) $ 645.1 $ (7.8 ) $ 736.0 $ (8.0 ) 75 U.S. agency 1.4 — 14.8 (0.1 ) 16.2 (0.1 ) 7 Municipal — — 25.4 (0.2 ) 25.4 (0.2 ) 8 Corporate 27.8 (0.1 ) 966.9 (10.7 ) 994.7 (10.8 ) 380 Non-U.S. government-backed corporate — — 28.1 (0.2 ) 28.1 (0.2 ) 10 Non-U.S. government 5.7 — 53.2 (0.2 ) 58.9 (0.2 ) 35 Asset-backed — — 13.1 (0.1 ) 13.1 (0.1 ) 6 Agency mortgage-backed 28.5 (0.1 ) 496.6 (10.1 ) 525.1 (10.2 ) 197 Total fixed income securities — Available for sale 154.3 (0.4 ) 2,243.2 (29.4 ) 2,397.5 (29.8 ) 718 Total short-term investments — Available for sale 17.2 — — — 17.2 — 7 Total $ 171.5 $ (0.4 ) $ 2,243.2 $ (29.4 ) $ 2,414.7 $ (29.8 ) 725 As at December 31, 2018 0-12 months Over 12 months Total Fair Market Value Gross Unrealized Loss Fair Market Value Gross Unrealized Loss Fair Market Value Gross Unrealized Loss Number of Securities ($ in millions) U.S. government $ 180.2 $ (0.7 ) $ 740.6 $ (15.4 ) $ 920.8 $ (16.1 ) 103 U.S. agency 13.5 (0.2 ) 18.4 (0.2 ) 31.9 (0.4 ) 12 Municipal 3.1 (0.1 ) 25.0 (0.7 ) 28.1 (0.8 ) 9 Corporate 999.1 (15.2 ) 762.2 (25.3 ) 1,761.3 (40.5 ) 667 Non-U.S. government-backed corporate 14.5 — 25.8 (0.2 ) 40.3 (0.2 ) 12 Non-U.S. government 64.0 (0.3 ) 91.0 (0.5 ) 155.0 (0.8 ) 57 Asset-backed 6.3 — 10.8 (0.1 ) 17.1 (0.1 ) 8 Agency mortgage-backed 245.7 (2.6 ) 447.3 (16.4 ) 693.0 (19.0 ) 253 Total fixed income securities — Available for sale 1,526.4 (19.1 ) 2,121.1 (58.8 ) 3,647.5 (77.9 ) 1,121 Total short-term investments — Available for sale 34.5 — — — 34.5 — 12 Total $ 1,560.9 $ (19.1 ) $ 2,121.1 $ (58.8 ) $ 3,682.0 $ (77.9 ) 1,133

Variable Interest Entities (Tab

Variable Interest Entities (Tables)	3 Months Ended
	Mar. 31, 2019
Payables and Accruals [Abstract]
Summary of Silverton Loan Notes	The following tables show the total liability balance of the Loan Notes for the three months ended March 31, 2019 and 2018 : For the Three Months Ended March 31, 2019 Third Party Aspen Holdings Total ($ in millions) Opening balance $ 4.6 $ 20.6 $ 25.2 Total change in fair value for the period 1.5 0.4 1.9 Total distributed in the period (0.2 ) (19.6 ) (19.8 ) Closing balance as at March 31, 2019 $ 5.9 $ 1.4 $ 7.3 Liability Loan notes (long-term liabilities) $ — $ — $ — Accrued expenses (current liabilities) 5.9 1.4 7.3 Total aggregate unpaid balance as at March 31, 2019 $ 5.9 $ 1.4 $ 7.3 For the Three Months Ended March 31, 2018 Third Party Aspen Holdings Total ($ in millions) Opening balance $ 86.6 $ 20.6 $ 107.2 Total change in fair value for the period (1.0 ) (0.3 ) (1.3 ) Total distributed in the period (45.8 ) (10.7 ) (56.5 ) Closing balance as at March 31, 2018 $ 39.8 $ 9.6 $ 49.4 Liability Loan notes (long-term liabilities) $ 32.2 $ 7.7 $ 39.9 Accrued expenses (current liabilities) 7.6 1.9 9.5 Total aggregate unpaid balance as at March 31, 2018 $ 39.8 $ 9.6 $ 49.4

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Financial Assets Measured on Recurring Basis	The following tables present the level within the fair value hierarchy at which the Company’s financial assets and liabilities are measured on a recurring basis as at March 31, 2019 and December 31, 2018 : As at March 31, 2019 Level 1 Level 2 Level 3 Total ($ in millions) Available for sale financial assets, at fair value U.S. government $ 1,359.1 $ — $ — $ 1,359.1 U.S. agency — 39.5 — 39.5 Municipal — 48.2 — 48.2 Corporate — 2,162.7 — 2,162.7 Non-U.S. government-backed corporate — 98.3 — 98.3 Non-U.S. government 224.6 137.0 — 361.6 Asset-backed — 16.1 — 16.1 Agency mortgage-backed — 955.0 — 955.0 Total fixed income securities available for sale, at fair value 1,583.7 3,456.8 — 5,040.5 Short-term investments available for sale, at fair value 149.4 11.5 — 160.9 Held for trading financial assets, at fair value U.S. government 218.8 — — 218.8 Municipal — 3.0 — 3.0 Corporate — 763.9 — 763.9 Non-U.S. government 48.9 203.6 — 252.5 Asset-backed — 2.3 — 2.3 Agency mortgage-backed — 48.8 — 48.8 Total fixed income securities trading, at fair value 267.7 1,021.6 — 1,289.3 Short-term investments trading, at fair value 76.8 4.2 — 81.0 Catastrophe bonds trading, at fair value — 38.1 — 38.1 Other investments (1) — — — 104.0 Other financial assets and liabilities, at fair value Derivatives at fair value — foreign exchange contracts — 10.8 — 10.8 Liabilities under derivative contracts — foreign exchange contracts — (7.2 ) — (7.2 ) Liabilities under derivative contracts — interest rate swaps — (49.5 ) — (49.5 ) Loan notes issued by variable interest entities, at fair value (included within accrued expenses and other payables) — — (5.9 ) (5.9 ) Total $ 2,077.6 $ 4,486.3 $ (5.9 ) $ 6,662.0 (1) Other investments represents our investment in a real estate fund and is measured at fair value using the net asset value per share practical expedient. As a result this has not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the condensed consolidated balance sheets. The investment in the real estate fund is subject to restrictions as detailed in Note 17. Transfers of assets into or out of a particular level are recorded at their fair values as of the end of each reporting period, consistent with the date of the determination of fair value. There were no significant transfers between Level 1, Level 2 and Level 3 during the three months ended March 31, 2019 . The Company settled $0.2 million of Level 3 liabilities in respect of the Loan Notes issued by Silverton for the three months ended March 31, 2019 . As at March 31, 2019 , there were no the assets classified as Level 3 and the Company’s Level 3 liabilities consisted solely of the Loan Notes issued by Silverton. As at December 31, 2018 Level 1 Level 2 Level 3 Total ($ in millions) Available for sale financial assets, at fair value U.S. government $ 1,404.2 $ — $ — $ 1,404.2 U.S. agency — 47.4 — 47.4 Municipal — 47.2 — 47.2 Corporate — 2,206.2 — 2,206.2 Non-U.S. government-backed corporate — 93.2 — 93.2 Non-U.S. government 268.0 134.6 — 402.6 Asset-backed — 17.3 — 17.3 Agency mortgage-backed — 1,012.6 — 1,012.6 Total fixed income securities available for sale, at fair value 1,672.2 3,558.5 — 5,230.7 Short-term investments available for sale, at fair value 93.7 11.9 — 105.6 Held for trading financial assets, at fair value U.S. government 147.7 — — 147.7 Municipal — 2.7 — 2.7 Corporate — 720.2 — 720.2 Non-U.S. government 68.2 197.2 — 265.4 Asset-backed — 2.4 — 2.4 Agency mortgage-backed — 49.4 — 49.4 Total fixed income securities trading, at fair value 215.9 971.9 — 1,187.8 Short-term investments trading, at fair value 4.5 5.0 — 9.5 Catastrophe bonds trading, at fair value — 36.2 — 36.2 Other investments (1) — — — 102.5 Other financial assets and liabilities, at fair value Derivatives at fair value – foreign exchange contracts — 14.6 — 14.6 Liabilities under derivative contracts – foreign exchange contracts — (15.1 ) — (15.1 ) Loan notes issued by variable interest entities, at fair value (included within accrued expenses and other payables) — — (4.6 ) (4.6 ) Total $ 1,986.3 $ 4,583.0 $ (4.6 ) $ 6,667.2
Reconciliation of Liabilities Using Level 3 Inputs	The following table presents a reconciliation of the beginning and ending balances for all assets and liabilities measured at fair value on a recurring basis using Level 3 inputs for the three months ended March 31, 2019 and 2018 : Reconciliation of Liabilities Using Level 3 Inputs Three Months Ended March 31, 2019 Three Months Ended March 31, 2018 ($ in millions) Balance at the beginning of the period $ 4.6 $ 86.6 Distributed to third party (0.2 ) (45.8 ) Total change in fair value included in the statement of operations 1.5 (1.0 ) Balance at the end of the period (1) $ 5.9 $ 39.8
Pricing Sources Used in Pricing Fixed Income Investments	Pricing sources used in pricing fixed income investments as at March 31, 2019 and December 31, 2018 were as follows: As at March 31, 2019 As at December 31, 2018 Index providers 84 % 84 % Pricing services 14 13 Broker-dealers 2 3 Total 100 % 100 %
Summary of Securities Priced Using Pricing Information from Index Providers	A summary of securities priced using pricing information from index providers as at March 31, 2019 and December 31, 2018 is provided below: As at March 31, 2019 As at December 31, 2018 Fair Market Value Determined using Prices from Index Providers % of Total Fair Value by Security Type Fair Market Value Determined using Prices from Index Providers % of Total Fair Value by Security Type ($ in millions, except for percentages) U.S. government $ 1,577.9 100 % $ 1,551.9 100 % U.S. agency 38.3 97 % 45.7 96 % Municipal 15.5 30 % 14.7 30 % Corporate 2,755.9 94 % 2,775.7 95 % Non-U.S. government-backed corporate 44.1 45 % 43.3 47 % Non-U.S. government 368.2 60 % 366.1 56 % Asset-backed 7.8 42 % 7.7 39 % Agency mortgage-backed 532.2 53 % 567.5 53 % Total fixed income securities $ 5,339.9 84 % $ 5,372.6 84 %
Fair Value Inputs, Assets, Quantitative Information	The observable and unobservable inputs used to determine the fair value of the Loan Notes as at March 31, 2019 and December 31, 2018 are presented in the tables below: As at March 31, 2019 Fair Value Level 3 Valuation Method Observable (O) and Unobservable (U) inputs Low High ($ in millions) ($ in millions) Loan Notes $ 5.9 (1) Internal Valuation Model Gross premiums written (O) $ 50.1 $ 61.1 Reserve for losses (U) $ 4.2 $ 61.9 Contract period (O) N/A 365 days Initial value of issuance (O) $ 325.0 $ 325.0 As at December 31, 2018 Fair Value Level 3 Valuation Method Observable (O) and Unobservable (U) inputs Low High ($ in millions) ($ in millions) Loan Notes $ 4.6 (1) Internal Valuation Model Gross premiums written (O) $ 50.1 $ 61.1 Reserve for losses (U) $ 4.2 $ 61.9 Contract period (O) N/A 365 days Initial value of issuance (O) $ 325.0 $ 325.0 (1) The amounts classified within accrued expenses and other payables were $5.9 million and $4.6 million as at March 31, 2019 and December 31, 2018 , respectively.

Derivative Contracts (Tables)

Derivative Contracts (Tables)	3 Months Ended
	Mar. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Fair Value of Derivative Instruments	The following tables summarize information on the location and amounts of derivative fair values on the consolidated balance sheet as at March 31, 2019 and December 31, 2018 : As at March 31, 2019 As at December 31, 2018 Derivatives Not Designated as Hedging Instruments Under ASC 815 Balance Sheet Location Notional Amount Fair Value Notional Amount Fair Value ($ in millions) ($ in millions) Foreign Exchange Contracts Derivatives at Fair Value $ 667.6 $ 8.9 $ 496.5 $ 14.6 Foreign Exchange Contracts Liabilities under Derivative Contracts $ 606.5 $ (7.2 ) (1) $ 760.8 $ (13.9 ) Interest Rate Swaps Liabilities under Derivative Contracts $ 3,318.0 $ (49.5 ) (2) $ — $ — (1) Net of $2.3 million cash collateral ( December 31, 2018 — $2.3 million ). (2) Initial and variation margin of $109.1 million has been posted ( December 31, 2018 — $ Nil ). As at March 31, 2019 As at December 31, 2018 Derivatives Designated as Hedging Instruments Under ASC 815 Balance Sheet Location Notional Amount Fair Value Notional Amount Fair Value ($ in millions) ($ in millions) Foreign Exchange Contracts Derivatives at Fair Value $ 70.8 $ 1.9 $ — $ — Foreign Exchange Contracts Liabilities under Derivative Contracts $ — $ — $ 94.3 $ (1.2 )
Gain/(Loss) Recognized in Income on Derivative	The following table provides the unrealized and realized gains recorded in the statements of operations and other comprehensive income for derivatives that are not designated or designated as hedging instruments under ASC 815 - “Derivatives and Hedging” for the three months ended March 31, 2019 and 2018 . Amount of Gain Recognized on Derivatives Three Months Ended Location of Gain Recognized on Derivatives March 31, 2019 March 31, 2018 Derivatives not designated as hedges ($ in millions) Foreign Exchange Contracts Change in Fair Value of Derivatives (3.1 ) 23.5 Interest Rate Swaps Change in Fair Value of Derivatives (50.2 ) — Derivatives designated as hedges Foreign Exchange Contracts General, administrative and corporate expenses 0.4 1.7 Foreign Exchange Contracts Net change from current period hedged transactions 1.7 0.9

Deferred Policy Acquisition C_2

Deferred Policy Acquisition Costs (Tables)	3 Months Ended
	Mar. 31, 2019
Insurance [Abstract]
Reconciliation of Beginning and Ending Deferred Policy Acquisition Costs	The following table represents a reconciliation of beginning and ending deferred policy acquisition costs for the three months ended March 31, 2019 and 2018 : Three Months Ended March 31, 2019 2018 ($ in millions) Balance at the beginning of the period $ 248.5 $ 294.3 Acquisition costs deferred 128.1 116.4 Amortization of deferred policy acquisition costs (88.2 ) (90.8 ) Balance at the end of the period $ 288.4 $ 319.9

Reserves for Losses and Loss _2

Reserves for Losses and Loss Adjustment Expenses (Tables)	3 Months Ended
	Mar. 31, 2019
Insurance [Abstract]
Reconciliation of Beginning and Ending Consolidated Loss and Loss Adjustment Expenses Reserves	The following table represents a reconciliation of beginning and ending consolidated loss and loss adjustment expenses (“LAE”) reserves for the three months ended March 31, 2019 and 2018 and the twelve months ended December 31, 2018 : Three Months Ended March 31, 2019 Three Months Ended March 31, 2018 Twelve Months Ended December 31, 2018 ($ in millions) Provision for losses and LAE at the start of the year $ 7,074.2 $ 6,749.5 $ 6,749.5 Less reinsurance recoverable (2,077.6 ) (1,515.2 ) (1,515.2 ) Net loss and LAE at the start of the year 4,996.6 5,234.3 5,234.3 Provision for losses and LAE for claims incurred: Current year 304.2 347.9 1,684.1 Prior years 7.6 (37.7 ) (111.1 ) Total incurred 311.8 310.2 1,573.0 Losses and LAE payments for claims incurred: Current year (7.1 ) (7.4 ) (285.7 ) Prior years (474.8 ) (483.7 ) (1,441.0 ) Total paid (481.9 ) (491.1 ) (1,726.7 ) Foreign exchange losses/(gains) 50.9 14.7 (84.0 ) Net losses and LAE reserves at period end 4,877.4 5,068.1 4,996.6 Plus reinsurance recoverable on unpaid losses at period end 2,122.9 1,611.3 2,077.6 Provision for losses and LAE at the end of the relevant period $ 7,000.3 $ 6,679.4 $ 7,074.2

Capital Structure (Tables)

Capital Structure (Tables)	3 Months Ended
	Mar. 31, 2019
Equity [Abstract]
Summary of Authorized and Issued Share Capital	The following table provides a summary of the Company’s authorized and issued share capital as at March 31, 2019 and December 31, 2018 : As at March 31, 2019 As at December 31, 2018 Number $ in Thousands Number $ in Thousands Authorized share capital: Ordinary Shares $0.01 per share (2018: 0.15144558¢ per share) 70,000,000 700 969,629,030 1,469 Non-Voting Shares 0.15144558¢ per share — — 6,787,880 10 Preference Shares 0.15144558¢ per share 30,000,000 45 100,000,000 152 Total authorized share capital 745 1,631 Issued share capital: Issued ordinary shares of $0.01 per share (2018: 0.15144558¢ per share) 60,395,839 604 59,743,156 90 Issued 5.95% preference shares of 0.15144558¢ each with a liquidation preference of $25 per share 11,000,000 17 11,000,000 17 Issued 5.625% preference shares of 0.15144558¢ each with a liquidation preference of $25 per share 10,000,000 15 10,000,000 15 Total issued share capital 636 122
Summary of Ordinary Shares	The following table summarizes transactions in the Company’s ordinary shares during the three months ended March 31, 2019 : Number of Ordinary Shares Ordinary shares of 0.015144558c per share Ordinary shares in issue as at December 31, 2018 59,743,156 Ordinary shares issued to employees under the 2013 share incentive plan and/or 2008 share purchase plan 144,269 Ordinary shares issued to non-employee directors 6,993 Ordinary shares canceled (59,894,418 ) Total ordinary shares of 0.015144558c per share in issue — Ordinary shares of $0.01 per share New ordinary shares issued of $0.01 per share 60,395,839 Ordinary shares in issue as at March 31, 2019 60,395,839

Intangible Assets and Goodwill

Intangible Assets and Goodwill (Tables)	3 Months Ended
	Mar. 31, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Summary of Changes in Intangible Assets	The following tables provide a summary of the Company’s intangible assets for the three months ended March 31, 2019 and 2018 : Three Months Ended March 31, 2019 Three Months Ended March 31, 2018 Beginning of the Period Additions Amortization End of the Period Beginning of the Period Additions Amortization End of the Period ($ in millions) ($ in millions) Intangible Assets Trademarks $ 2.5 $ — $ (0.1 ) $ 2.4 $ 2.9 $ — $ (0.1 ) $ 2.8 Insurance Licenses 16.7 — — 16.7 16.7 — — 16.7 Agency Relationships 1.8 — (0.1 ) 1.7 2.3 — (0.1 ) 2.2 Non-compete Agreements 0.4 — (0.1 ) 0.3 0.7 — (0.1 ) 0.6 Goodwill 3.9 — — 3.9 3.9 — — 3.9 Renewal Rights 1.0 — (0.1 ) 0.9 1.4 — (0.1 ) 1.3 Total $ 26.3 $ — $ (0.4 ) $ 25.9 $ 27.9 $ — $ (0.4 ) $ 27.5

Operating Leases (Tables)

Operating Leases (Tables)	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Lease, Cost	Operating lease charge. The following table summarizes the operating lease charge for the three months ended March 31, 2019 : For the Three Months Ended March 31, 2019 ($ in millions) Amortization charge on Right-of-use operating leased assets $ 3.3 Interest on operating lease liabilities $ 1.2 Operating lease charge $ 4.5
Lessee, Operating Lease, Liability	Lease Liabilities. The following table summarizes the maturity of lease liabilities under non-cancellable leases as of March 31, 2019 : March 31, 2019 ($ in millions) Operating leases - maturities 2019 $ 12.9 2020 $ 14.2 2021 $ 11.8 2022 $ 9.4 2023 $ 8.9 Later years $ 64.5 Total minimum lease payments $ 121.7 Less imputed interest $ (27.8 ) Total lease liabilities $ 93.9
Summary of Other Lease Information	Other lease information. The following table summarizes the cash flows on operating leases for the three months ended March 31, 2019 and other supplemental information: For the Three Months Ended March 31, 2019 ($ in millions) Cash paid for amounts included in the measurement of lease liabilities - Operating cash outflow from operating leases $ (4.5 ) Right-of-use assets obtained in exchange for lease obligations - Operating leases $ 3.1 Reduction to Right-of-use assets resulting from reductions to lease obligations - Operating leases $ 1.2 Weighted Averages - Operating leases, remaining lease terms (years) 10.5 - Operating leases, average discount rate 5.0 %

Commitments and Contingent Li_2

Commitments and Contingent Liabilities (Tables)	3 Months Ended
	Mar. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Schedule of Company's Restricted Assets	The following table details the forms and value of the Company’s restricted assets as at March 31, 2019 and December 31, 2018 : As at March 31, 2019 As at December 31, 2018 ($ in millions, except percentages) Regulatory trusts and deposits: Affiliated transactions $ 922.5 $ 1,033.9 Third party 2,745.7 2,511.7 Letters of credit / guarantees (1) 792.4 771.1 Investment commitment — real estate fund — — Other investments — real estate fund 104.0 102.5 Total restricted assets $ 4,564.6 $ 4,419.2 Total as percent of investable assets (2) 58.5 % 56.4 % (1) As at March 31, 2019 , the Company had pledged funds in the amount of $792.4 million ( December 31, 2018 — $771.1 million ) as collateral for the secured letters of credit. (2) Investable assets comprise total investments, cash and cash equivalents, accrued interest, receivables for securities sold and payables for securities purchased.

History, Organization and Bus_2

History, Organization and Business Combination - Narrative (Details) - USD ($)	Mar. 31, 2019		Feb. 15, 2019	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Business acquisition, share price			$ 42.75
Authorized Share Capital	$ 745,434			$ 1,631,000
Number of ordinary shares (in shares)	70,000,000			969,629,030
Ordinary shares, par value (in usd per share)	$ 0.01	[1]		$ 0.0015144558
Ordinary shares, issued (in shares)	60,395,839			59,743,156
Number of preference shares (in shares)	30,000,000			100,000,000
[1]	On February 15, 2019, the Company completed its previously announced merger (the “Merger”) with Highlands Merger Sub, Ltd. (“Merger Sub”), a wholly owned subsidiary of Highlands Holdings, Ltd. (“Parent”). As a result of the Merger, a change in control of the Company occurred and the Company is now a wholly owned subsidiary of Parent. At the effective time of the Merger, each of the Company’s issued and outstanding ordinary shares (other than ordinary shares owned by the Company as treasury shares, owned by any subsidiary of the Company or owned by Parent, Merger Sub or any subsidiary thereof) was automatically canceled and converted into the right to receive $42.75 in cash, without interest and less any required tax withholdings. The ordinary shares of the Company ceased trading on the New York Stock Exchange prior to the opening of trading on February 15, 2019. Therefore, earnings per share data is no longer considered meaningful for both the current reporting period and for the comparative period and has been excluded. For more information on the Merger, refer to Note 1 of these unaudited condensed consolidated financial statements.

History, Organization and Bus_3

History, Organization and Business Combination - Class of Stock (Details) - $ / shares	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Sep. 20, 2016
Class of Stock [Line Items]
Preference shares, par value (in usd per share)	$ 0.0015144558	$ 0.0015144558
5.95% preference shares
Class of Stock [Line Items]
Preference shares, rate	5.95%	5.95%
Preference shares, issued (in shares)	11,000,000	11,000,000
Preference shares, par value (in usd per share)	$ 0.0015144558	$ 0.0015144558
5.625% preference shares
Class of Stock [Line Items]
Preference shares, rate	5.625%	5.625%
Preference shares, issued (in shares)	10,000,000	10,000,000	10,000,000
Preference shares, par value (in usd per share)	$ 0.0015144558	$ 0.0015144558

Basis of Preparation - Narrativ

Basis of Preparation - Narrative (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018	Jan. 01, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right-of-use operating lease assets		$ 91.4			$ 0
Operating lease liabilities		$ 93.9		$ 93.6	$ 0
Weighted average incremental borrowing rate (percent)		5.00%
Asset obtained in exchange for operating lease liability		$ 3.1
Operating lease charge		(4.5)	$ 0
Amortization of right-of-use operating lease assets		(3.3)	0
Interest on operating lease liabilities		(1.2)
Accounting Standards Update 2016-09 | Retained earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption	[1]	$ (2.4)	$ 0
Leased office real estate and motor vehicles
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right-of-use operating lease assets				$ 91.2
[1]	The $2.4 million relates to the cumulative effect-adjustment to opening retained earnings as a result of the recognition of operating lease right-of-use assets and corresponding liabilities on the balance sheet following the adoption of ASU 2016-02. The adjustment has been applied using a modified retrospective approach.

Reclassifications from Accumu_3

Reclassifications from Accumulated Other Comprehensive Income - Schedule of Accumulated Other Comprehensive Income Reclassification (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Available for sale securities:
Income from operations before income tax	$ 6.2	$ 34.4
General, administrative and corporate expenses	137.3	121
Income tax benefit/(expense)	4.4	(3.6)
Net income	10.6	30.8
Reclassification out of AOCI
Available for sale securities:
Net income	0.1	1.4
Reclassification out of AOCI | Available for sale securities
Available for sale securities:
Realized gains on sale of securities	3	2
Realized (losses) on sale of securities	(3.2)	(1.9)
Income from operations before income tax	(0.2)	0.1
Income tax benefit/(expense)	0	(0.1)
Net income	(0.2)	0
Reclassification out of AOCI | Realized derivatives
Available for sale securities:
General, administrative and corporate expenses	0.4	1.7
Income tax benefit/(expense)	(0.1)	(0.3)
Net income	$ 0.3	$ 1.4

Dividends - Summary of Declared

Dividends - Summary of Declared Dividends (Details) - $ / shares	May 01, 2019	Mar. 31, 2019	Dec. 31, 2018
5.95% preference shares
Dividends Payable [Line Items]
Preference shares, rate		5.95%	5.95%
5.625% preference shares
Dividends Payable [Line Items]
Preference shares, rate		5.625%	5.625%
Subsequent Event | 5.95% preference shares
Dividends Payable [Line Items]
Dividend (in usd per share)	$ 0.3719
Payable Date	Jul. 1, 2019
Record Date	Jun. 15, 2019
Subsequent Event | 5.625% preference shares
Dividends Payable [Line Items]
Dividend (in usd per share)	$ 0.3516
Payable Date	Jul. 1, 2019
Record Date	Jun. 15, 2019

Segment Reporting - Narrative (

Segment Reporting - Narrative (Details)	3 Months Ended
	Mar. 31, 2019Segment
Segment Reporting [Abstract]
Number of business segments	2

Segment Reporting - Summary of

Segment Reporting - Summary of Gross and Net Written and Earned Premiums, Underwriting Results, Ratios and Reserves for Each of Company's Business Segments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Underwriting Revenues
Gross written premiums	$ 1,013.8	$ 1,116.8
Net written premiums	617.6	635.5
Gross earned premiums	817	842.6
Net earned premiums	510.6	533.5
Underwriting Expenses
Losses and loss adjustment expenses	311.8	310.2
Amortization of deferred policy acquisition costs	88.2	90.8
General and administrative expenses	86.2	95.2
Underwriting income	24.4	37.3
Corporate expenses	(11.9)	(13.7)
Non-operating income (expense)	(39.2)	(12.1)
Net investment income	51.5	47.3
Realized and unrealized investment gains	42	100.6
Realized and unrealized investment losses	(6.2)	(138.3)
Change in fair value of loan notes issued by variable interest entities	(1.5)	1
Change in fair value of derivatives	(53.3)	23.5
Interest expense on long term debt	(5.5)	(7.4)
Net realized and unrealized foreign exchange gains	5.1	(4.7)
Other income	1.7	2.1
Other expenses	(0.9)	(1.2)
Income from operations before income tax	6.2	34.4
Net reserves for loss and loss adjustment expenses	$ 4,877.4	$ 5,068.1	$ 4,996.6	$ 5,234.3
Ratios
Loss ratio	61.10%	58.10%
Policy acquisition expense ratio	17.30%	17.00%
General and administrative expense ratio	26.90%	22.70%
Expense ratio	44.20%	39.70%
Combined ratio	105.30%	97.80%
Non-operating expenses related to Effectiveness and Efficiency Program	$ 6.1	$ 11.8
Non-operating expenses related to Merger Agreement	29.8
Reinsurance
Underwriting Revenues
Gross written premiums	538.4	623.5
Net written premiums	395.6	425
Gross earned premiums	336.5	375
Net earned premiums	276.9	282.5
Underwriting Expenses
Losses and loss adjustment expenses	165.8	166.9
Amortization of deferred policy acquisition costs	62.6	55.9
General and administrative expenses	27.2	31.6
Underwriting income	21.3	28.1
Net reserves for loss and loss adjustment expenses	$ 2,871.5	$ 2,823.6
Ratios
Loss ratio	59.90%	59.10%
Policy acquisition expense ratio	22.60%	19.80%
General and administrative expense ratio	9.80%	11.20%
Expense ratio	32.40%	31.00%
Combined ratio	92.30%	90.10%
Insurance
Underwriting Revenues
Gross written premiums	$ 475.4	$ 493.3
Net written premiums	222	210.5
Gross earned premiums	480.5	467.6
Net earned premiums	233.7	251
Underwriting Expenses
Losses and loss adjustment expenses	146	143.3
Amortization of deferred policy acquisition costs	25.6	34.9
General and administrative expenses	59	63.6
Underwriting income	3.1	9.2
Net reserves for loss and loss adjustment expenses	$ 2,005.9	$ 2,244.5
Ratios
Loss ratio	62.50%	57.10%
Policy acquisition expense ratio	11.00%	13.90%
General and administrative expense ratio	25.20%	25.30%
Expense ratio	36.20%	39.20%
Combined ratio	98.70%	96.30%

Investments - Summary of Invest

Investments - Summary of Investment Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 53.7	$ 49.9
Investment expenses	(2.2)	(2.6)
Net investment income	51.5	47.3
Total fixed income securities — Available for sale
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	34.3	33.3
Short-term investments
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	0.8	0.2
Short-term Investment, Trading
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	0.2	0.2
Fixed term deposits (included in cash and cash equivalents)
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	4.5	2.4
Equity securities — Trading
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	0	1.2
Catastrophe bonds — Trading
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	0.8	0.6
Other investments, at fair value
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	1.4	0
Fixed income maturities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 11.7	$ 12

Investments - Net Realized and

Investments - Net Realized and Unrealized Investment Gains and Losses and Change in Unrealized Gains and Losses on Investments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Fixed income securities, available for sale — gross realized gains	$ 3	$ 1.8
Fixed income securities, available for sale — gross realized (losses)	(3.2)	(1.8)
Other-than-temporary impairments	0	0
Fixed income securities, trading - gross realized gains	2.3	1.6
Fixed income securities, trading - gross realized (losses)	(2.8)	(7)
Equity securities — gross realized gains	0	94.5
Equity securities — gross realized (losses)	0	(20.3)
Catastrophe bonds	0.3	0.9
Net change in gross unrealized gains/(losses)	36.3	(108.8)
Total net realized and unrealized investment gains/(losses) recorded in the statement of operations	35.8	(37.7)
Change in available for sale net unrealized gains/(losses):
Fixed income securities	75.6	(82.9)
Change in taxes	(5.2)	5.5
Total change in net unrealized gains/(losses), net of taxes, recorded in other comprehensive income	70.4	(77.4)
Short-term investments
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Fixed income securities, trading - gross realized (losses)	(0.1)	0
Cash and cash equivalents
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Fixed income securities, available for sale — gross realized gains	0	0.2
Fixed income securities, available for sale — gross realized (losses)	0	(0.1)
Fixed income securities, trading - gross realized gains	0.1	1.6
MVI
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Change in fair value of investment	0	(0.1)
Bene
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Change in fair value of investment	$ (0.1)	$ (0.2)

Investments - Cost, Gross Unrea

Investments - Cost, Gross Unrealized Gains and Losses, and Estimated Fair Value of Available for Sale Investments in Fixed Income Maturities, Short-Term Investments and Equities (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Statement [Line Items]
Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost	$ 5,177.2	$ 5,387.9
Gross Unrealized Gains	54	26.3
Gross Unrealized Losses	(29.8)	(77.9)
Fair Market Value	5,201.4	5,336.3
Total fixed income securities — Available for sale
Statement [Line Items]
Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost	5,016.5	5,282.3
Gross Unrealized Gains	53.8	26.3
Gross Unrealized Losses	(29.8)	(77.9)
Fair Market Value	5,040.5	5,230.7
Total short-term investments — Available for sale
Statement [Line Items]
Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost	160.7	105.6
Gross Unrealized Gains	0.2	0
Gross Unrealized Losses	0	0
Fair Market Value	160.9	105.6
U.S. government
Statement [Line Items]
Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost	1,352.6	1,413.5
Gross Unrealized Gains	14.6	6.8
Gross Unrealized Losses	(8)	(16.1)
Fair Market Value	1,359.2	1,404.2
U.S. agency
Statement [Line Items]
Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost	39.3	47.7
Gross Unrealized Gains	0.3	0.1
Gross Unrealized Losses	(0.1)	(0.4)
Fair Market Value	39.5	47.4
Municipal
Statement [Line Items]
Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost	46.5	46.7
Gross Unrealized Gains	1.9	1.3
Gross Unrealized Losses	(0.2)	(0.8)
Fair Market Value	48.2	47.2
Corporate
Statement [Line Items]
Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost	2,151.6	2,238.9
Gross Unrealized Gains	21.8	7.8
Gross Unrealized Losses	(10.8)	(40.5)
Fair Market Value	2,162.6	2,206.2
Non-U.S. government-backed corporate
Statement [Line Items]
Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost	98.1	93.2
Gross Unrealized Gains	0.4	0.2
Gross Unrealized Losses	(0.2)	(0.2)
Fair Market Value	98.3	93.2
Non-U.S. government
Statement [Line Items]
Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost	356.9	399.8
Gross Unrealized Gains	4.9	3.6
Gross Unrealized Losses	(0.2)	(0.8)
Fair Market Value	361.6	402.6
Asset-backed
Statement [Line Items]
Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost	16.2	17.4
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(0.1)	(0.1)
Fair Market Value	16.1	17.3
Agency mortgage-backed
Statement [Line Items]
Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost	955.3	1,025.1
Gross Unrealized Gains	9.9	6.5
Gross Unrealized Losses	(10.2)	(19)
Fair Market Value	$ 955	$ 1,012.6

Investments - Cost, Gross Unr_2

Investments - Cost, Gross Unrealized Gains and Losses, and Estimated Fair Value of Trading Investments in Fixed Income Maturities (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Statement [Line Items]
Cost or Amortized Cost	$ 1,273.1	$ 1,205
Fair Market Value	1,289.3	1,187.8
U.S. government
Statement [Line Items]
Cost or Amortized Cost	217.4	146.6
Gross Unrealized Gains	1.6	1.6
Gross Unrealized Losses	(0.2)	(0.5)
Fair Market Value	218.8	147.7
Municipal
Statement [Line Items]
Cost or Amortized Cost	3	2.8
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	(0.1)
Fair Market Value	3	2.7
Corporate
Statement [Line Items]
Cost or Amortized Cost	754.9	734.2
Gross Unrealized Gains	12.4	2.6
Gross Unrealized Losses	(3.4)	(16.6)
Fair Market Value	763.9	720.2
Non-U.S. government
Statement [Line Items]
Cost or Amortized Cost	246.4	268.7
Gross Unrealized Gains	6.8	1.9
Gross Unrealized Losses	(0.7)	(5.2)
Fair Market Value	252.5	265.4
Asset-backed
Statement [Line Items]
Cost or Amortized Cost	2.3	2.4
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Market Value	2.3	2.4
Agency mortgage-backed
Statement [Line Items]
Cost or Amortized Cost	49.1	50.3
Gross Unrealized Gains	0.3	0.2
Gross Unrealized Losses	(0.6)	(1.1)
Fair Market Value	48.8	49.4
Total fixed income securities — Trading
Statement [Line Items]
Cost or Amortized Cost	1,273.1	1,205
Gross Unrealized Gains	21.1	6.3
Gross Unrealized Losses	(4.9)	(23.5)
Fair Market Value	1,289.3	1,187.8
Total short-term investments — Trading
Statement [Line Items]
Cost or Amortized Cost	81	9.5
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Market Value	81	9.5
Total catastrophe bonds — Trading
Statement [Line Items]
Cost or Amortized Cost	39.5	37.9
Gross Unrealized Gains	0	0.1
Gross Unrealized Losses	(1.4)	(1.8)
Fair Market Value	38.1	36.2
Total
Statement [Line Items]
Cost or Amortized Cost	1,393.6	1,252.4
Gross Unrealized Gains	21.1	6.4
Gross Unrealized Losses	(6.3)	(25.3)
Fair Market Value	$ 1,408.4	$ 1,233.5

Investments - Other Investments

Investments - Other Investments (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Equity Method Investment, Aggregate Cost [Roll Forward]
Opening undistributed value of investment	$ 67.1
Investment in the period	0
Unrealized/realized gain/(loss)	(0.1)
Closing value of investment	67
MVI
Equity Method Investment, Aggregate Cost [Roll Forward]
Opening undistributed value of investment	0.5
Investment in the period	0
Unrealized/realized gain/(loss)	0
Closing value of investment	0.5
Bene
Equity Method Investment, Aggregate Cost [Roll Forward]
Opening undistributed value of investment	3.2
Investment in the period	0
Unrealized/realized gain/(loss)	(0.1)
Closing value of investment	3.1
Digital Re
Equity Method Investment, Aggregate Cost [Roll Forward]
Opening undistributed value of investment	0.9
Investment in the period	0
Unrealized/realized gain/(loss)	0
Closing value of investment	0.9
Crop Re
Equity Method Investment, Aggregate Cost [Roll Forward]
Opening undistributed value of investment	62.5
Investment in the period	0
Unrealized/realized gain/(loss)	0
Closing value of investment	$ 62.5

Investments - Summary of Fixed

Investments - Summary of Fixed Maturities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost	$ 5,177.2		$ 5,387.9
Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost	5,016.5		5,282.3
Available for sale investments in fixed income maturities, Fair Market Value	5,201.4		5,336.3
Total fixed income securities — Available for sale
Debt Securities, Available-for-sale [Line Items]
Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost	5,016.5		5,282.3
Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost	5,016.5		5,282.3
Available for sale investments in fixed income maturities, Fair Market Value	5,040.5		5,230.7
Agency mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost	955.3		1,025.1
Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost	955.3		1,025.1
Available for sale investments in fixed income maturities, Fair Market Value	$ 955		1,012.6
Available For Sale Securities Average Ratings By Maturity	AA+	AA+
Asset-backed
Debt Securities, Available-for-sale [Line Items]
Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost	$ 16.2		17.4
Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost	16.2		17.4
Available for sale investments in fixed income maturities, Fair Market Value	$ 16.1		17.3
Available For Sale Securities Average Ratings By Maturity	AAA	AAA
Total fixed income securities — Available for sale
Debt Securities, Available-for-sale [Line Items]
Due one year or less, Cost or Amortized Cost	$ 441.1		464.3
Due after one year through five years, Cost or Amortized Cost	2,463.8		2,605.7
Due after five years through ten years, Cost or Amortized Cost	1,014.7		1,047.9
Due after ten years, Cost or Amortized Cost	125.4		121.9
Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost	4,045		4,239.8
Due one year or less, Fair Market Value	440.7		463.5
Due after one year through five years, Fair Market Value	2,467		2,582
Due after five years through ten years, Fair Market Value	1,025.1		1,028.3
Due after ten years, Fair Market Value	136.6		127
Available for sale investments in fixed income maturities, Fair Market Value	$ 4,069.4		$ 4,200.8
Available For Sale Securities Average for one year or less	AA-	AA-
Available For Sale Securities Average after one year through five years	AA-	AA-
Available For Sale Securities Average after five years through ten years	AA-	AA-
Available For Sale Securities Debt Maturities After Ten Years Average Ratings By Maturity	AA-	AA-

Investments - Aggregate Fair Va

Investments - Aggregate Fair Value and Gross Unrealized Loss by Type of Security (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)Security	Dec. 31, 2018USD ($)Security
Debt Securities, Available-for-sale [Line Items]
Document Period End Date	Mar. 31, 2019
0-12 months, Fair Market Value	$ 171.5	$ 1,560.9
0-12 months, Gross Unrealized Loss	(0.4)	(19.1)
Over 12 months, Fair Market Value	2,243.2	2,121.1
Over 12 months, Gross Unrealized Loss	(29.4)	(58.8)
Total, Fair Market Value	2,414.7	3,682
Total, Gross Unrealized Loss	$ (29.8)	$ (77.9)
Number of Securities | Security	725	1,133
Total fixed income securities — Available for sale
Debt Securities, Available-for-sale [Line Items]
0-12 months, Fair Market Value	$ 154.3	$ 1,526.4
0-12 months, Gross Unrealized Loss	(0.4)	(19.1)
Over 12 months, Fair Market Value	2,243.2	2,121.1
Over 12 months, Gross Unrealized Loss	(29.4)	(58.8)
Total, Fair Market Value	2,397.5	3,647.5
Total, Gross Unrealized Loss	$ (29.8)	$ (77.9)
Number of Securities | Security	718	1,121
Total short-term investments — Trading
Debt Securities, Available-for-sale [Line Items]
0-12 months, Fair Market Value	$ 17.2	$ 34.5
0-12 months, Gross Unrealized Loss	0	0
Over 12 months, Fair Market Value	0	0
Over 12 months, Gross Unrealized Loss	0	0
Total, Fair Market Value	17.2	34.5
Total, Gross Unrealized Loss	$ 0	$ 0
Number of Securities | Security	7	12
U.S. government
Debt Securities, Available-for-sale [Line Items]
0-12 months, Fair Market Value	$ 90.9	$ 180.2
0-12 months, Gross Unrealized Loss	(0.2)	(0.7)
Over 12 months, Fair Market Value	645.1	740.6
Over 12 months, Gross Unrealized Loss	(7.8)	(15.4)
Total, Fair Market Value	736	920.8
Total, Gross Unrealized Loss	$ (8)	$ (16.1)
Number of Securities | Security	75	103
U.S. agency
Debt Securities, Available-for-sale [Line Items]
0-12 months, Fair Market Value	$ 1.4	$ 13.5
0-12 months, Gross Unrealized Loss	0	(0.2)
Over 12 months, Fair Market Value	14.8	18.4
Over 12 months, Gross Unrealized Loss	(0.1)	(0.2)
Total, Fair Market Value	16.2	31.9
Total, Gross Unrealized Loss	$ (0.1)	$ (0.4)
Number of Securities | Security	7	12
Municipal
Debt Securities, Available-for-sale [Line Items]
0-12 months, Fair Market Value	$ 0	$ 3.1
0-12 months, Gross Unrealized Loss	0	(0.1)
Over 12 months, Fair Market Value	25.4	25
Over 12 months, Gross Unrealized Loss	(0.2)	(0.7)
Total, Fair Market Value	25.4	28.1
Total, Gross Unrealized Loss	$ (0.2)	$ (0.8)
Number of Securities | Security	8	9
Corporate
Debt Securities, Available-for-sale [Line Items]
0-12 months, Fair Market Value	$ 27.8	$ 999.1
0-12 months, Gross Unrealized Loss	(0.1)	(15.2)
Over 12 months, Fair Market Value	966.9	762.2
Over 12 months, Gross Unrealized Loss	(10.7)	(25.3)
Total, Fair Market Value	994.7	1,761.3
Total, Gross Unrealized Loss	$ (10.8)	$ (40.5)
Number of Securities | Security	380	667
Non-U.S. government-backed corporate
Debt Securities, Available-for-sale [Line Items]
0-12 months, Fair Market Value	$ 0	$ 14.5
0-12 months, Gross Unrealized Loss	0	0
Over 12 months, Fair Market Value	28.1	25.8
Over 12 months, Gross Unrealized Loss	(0.2)	(0.2)
Total, Fair Market Value	28.1	40.3
Total, Gross Unrealized Loss	$ (0.2)	$ (0.2)
Number of Securities | Security	10	12
Non-U.S. government
Debt Securities, Available-for-sale [Line Items]
0-12 months, Fair Market Value	$ 5.7	$ 64
0-12 months, Gross Unrealized Loss	0	(0.3)
Over 12 months, Fair Market Value	53.2	91
Over 12 months, Gross Unrealized Loss	(0.2)	(0.5)
Total, Fair Market Value	58.9	155
Total, Gross Unrealized Loss	$ (0.2)	$ (0.8)
Number of Securities | Security	35	57
Asset-backed
Debt Securities, Available-for-sale [Line Items]
0-12 months, Fair Market Value	$ 0	$ 6.3
0-12 months, Gross Unrealized Loss	0	0
Over 12 months, Fair Market Value	13.1	10.8
Over 12 months, Gross Unrealized Loss	(0.1)	(0.1)
Total, Fair Market Value	13.1	17.1
Total, Gross Unrealized Loss	$ (0.1)	$ (0.1)
Number of Securities | Security	6	8
Agency mortgage-backed
Debt Securities, Available-for-sale [Line Items]
0-12 months, Fair Market Value	$ 28.5	$ 245.7
0-12 months, Gross Unrealized Loss	(0.1)	(2.6)
Over 12 months, Fair Market Value	496.6	447.3
Over 12 months, Gross Unrealized Loss	(10.1)	(16.4)
Total, Fair Market Value	525.1	693
Total, Gross Unrealized Loss	$ (10.2)	$ (19)
Number of Securities | Security	197	253

Investments - Narrative (Detail

Investments - Narrative (Details) - USD ($)	Dec. 18, 2017	Mar. 31, 2019	Mar. 31, 2018	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Sep. 19, 2018	Sep. 18, 2018	May 10, 2018	Dec. 20, 2017	Jan. 01, 2017	Jul. 26, 2016	Jan. 01, 2015
Investment Holdings [Line Items]
Catastrophe bonds		$ 38,100,000			$ 36,200,000
Equity method investment, aggregate cost		67,000,000			67,100,000
Restricted assets		4,564,600,000			4,419,200,000
Other investments		104,000,000			102,500,000
Investment funds		0			0
OTTI charge recognized		0	$ 0
MVI
Investment Holdings [Line Items]
Equity method investment, aggregate cost		500,000			500,000								$ 800,000
Additional investment				$ 100,000		$ 100,000
Bene
Investment Holdings [Line Items]
Equity method investment, aggregate cost		3,100,000			3,200,000							$ 3,300,000
Additional investment					1,200,000
Equity method investment, ownership percentage												20.00%
Digital Re
Investment Holdings [Line Items]
Equity method investment, aggregate cost		900,000			900,000						$ 2,300,000
Equity method investment, ownership percentage											49.00%
Crop Re
Investment Holdings [Line Items]
Equity method investment, aggregate cost	$ 62,500,000	62,500,000			62,500,000
Additional investment	$ 5,900,000
Equity method investment, ownership percentage	23.20%
AgriLogic Consulting, LLC
Investment Holdings [Line Items]
Equity method investment, aggregate cost								$ 0
Equity method investment, ownership percentage								40.00%
CGB DS | Crop Re
Investment Holdings [Line Items]
Equity method investment, counterparty ownership percentage	76.80%
Limited Partner | Real estate funds
Investment Holdings [Line Items]
Restricted assets		$ 0			$ 0					$ 100,000,000
Other investments							$ 13,800,000		$ 86,200,000
Disposed of by Sale | Consulting Relationships | AgriLogic Consulting, LLC
Investment Holdings [Line Items]
Sale of interest of consulting business								60.00%

Variable Interest Entities - Na

Variable Interest Entities - Narrative (Details)	Mar. 31, 2019variable_interest_entity
Payables and Accruals [Abstract]
Number of Variable Interest Entities	2

Variable Interest Entities - Su

Variable Interest Entities - Summary of Silverton Loan Notes (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Movement in Silverton Loan Notes [Roll Forward]
Total liability balance of Loan Notes, Beginning Balance	$ 25.2	$ 107.2
Total change in fair value for the period	(1.5)	1
Total distributed in the period	(19.8)	(56.5)
Total liability balance of Loan Notes, Ending Balance	7.3	49.4
Loan notes (long-term liabilities)			$ 0	$ 39.9
Accrued expenses (current liabilities)			7.3	9.5
Total aggregate unpaid balance	25.2	107.2	7.3	49.4
Third party
Movement in Silverton Loan Notes [Roll Forward]
Total liability balance of Loan Notes, Beginning Balance	4.6	86.6
Total change in fair value for the period	1.5	(1)
Total distributed in the period	(0.2)	(45.8)
Total liability balance of Loan Notes, Ending Balance	5.9	39.8
Loan notes (long-term liabilities)			0	32.2
Accrued expenses (current liabilities)			5.9	7.6
Total aggregate unpaid balance	4.6	86.6	5.9	39.8
Aspen Holdings
Movement in Silverton Loan Notes [Roll Forward]
Total liability balance of Loan Notes, Beginning Balance	20.6	20.6
Total change in fair value for the period	0.4	(0.3)
Total distributed in the period	(19.6)	(10.7)
Total liability balance of Loan Notes, Ending Balance	1.4	9.6
Loan notes (long-term liabilities)			0	7.7
Accrued expenses (current liabilities)			1.4	1.9
Total aggregate unpaid balance	20.6	20.6	$ 1.4	$ 9.6
Aspen Holdings | Third party
Movement in Silverton Loan Notes [Roll Forward]
Total change in fair value for the period	$ 1.9	$ (1.3)

Fair Value Measurements - Finan

Fair Value Measurements - Financial Assets Measured on Recurring Basis (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Catastrophe bonds trading, at fair value	$ 39.5	$ 37.9
Derivatives at fair value	10.8	14.6
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Catastrophe bonds trading, at fair value	38.1	36.2
Total	6,662	6,667.2
Fair Value, Measurements, Recurring | Short term investments, trading at fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	81	9.5
Fair Value, Measurements, Recurring | Derivatives at fair value, assets | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives at fair value	10.8	14.6
Fair Value, Measurements, Recurring | Derivatives at fair value, assets | Interest Rate Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities at fair value	(49.5)
Fair Value, Measurements, Recurring | Liabilities under derivative contracts — foreign exchange contracts | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities at fair value	(7.2)	(15.1)
Available for sale financial assets | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	5,040.5	5,230.7
Available for sale financial assets | Fair Value, Measurements, Recurring | U.S. government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	1,359.1	1,404.2
Available for sale financial assets | Fair Value, Measurements, Recurring | U.S. agency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	39.5	47.4
Available for sale financial assets | Fair Value, Measurements, Recurring | Municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	48.2	47.2
Available for sale financial assets | Fair Value, Measurements, Recurring | Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	2,162.7	2,206.2
Available for sale financial assets | Fair Value, Measurements, Recurring | Non-U.S. government-backed corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	98.3	93.2
Available for sale financial assets | Fair Value, Measurements, Recurring | Non-U.S. government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	361.6	402.6
Available for sale financial assets | Fair Value, Measurements, Recurring | Asset-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	16.1	17.3
Available for sale financial assets | Fair Value, Measurements, Recurring | Agency mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	955	1,012.6
Short-term investments | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	160.9	105.6
Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	1,289.3	1,187.8
Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | U.S. government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	218.8	147.7
Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	3	2.7
Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	763.9	720.2
Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Non-U.S. government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	252.5	265.4
Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Asset-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	2.3	2.4
Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Agency mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	48.8	49.4
Real estate funds | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	104	102.5
Level 1 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Catastrophe bonds trading, at fair value	0	0
Total	2,077.6	1,986.3
Level 1 | Fair Value, Measurements, Recurring | Short term investments, trading at fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	76.8	4.5
Level 1 | Fair Value, Measurements, Recurring | Derivatives at fair value, assets | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives at fair value	0	0
Level 1 | Fair Value, Measurements, Recurring | Derivatives at fair value, assets | Interest Rate Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities at fair value	0
Level 1 | Fair Value, Measurements, Recurring | Liabilities under derivative contracts — foreign exchange contracts | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities at fair value	0	0
Level 1 | Available for sale financial assets | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	1,583.7	1,672.2
Level 1 | Available for sale financial assets | Fair Value, Measurements, Recurring | U.S. government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	1,359.1	1,404.2
Level 1 | Available for sale financial assets | Fair Value, Measurements, Recurring | U.S. agency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Level 1 | Available for sale financial assets | Fair Value, Measurements, Recurring | Municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Level 1 | Available for sale financial assets | Fair Value, Measurements, Recurring | Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Level 1 | Available for sale financial assets | Fair Value, Measurements, Recurring | Non-U.S. government-backed corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Level 1 | Available for sale financial assets | Fair Value, Measurements, Recurring | Non-U.S. government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	224.6	268
Level 1 | Available for sale financial assets | Fair Value, Measurements, Recurring | Asset-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Level 1 | Available for sale financial assets | Fair Value, Measurements, Recurring | Agency mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Level 1 | Short-term investments | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	149.4	93.7
Level 1 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	267.7	215.9
Level 1 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | U.S. government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	218.8	147.7
Level 1 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Level 1 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Level 1 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Non-U.S. government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	48.9	68.2
Level 1 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Asset-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Level 1 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Agency mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Level 1 | Real estate funds | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Level 2 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Catastrophe bonds trading, at fair value	38.1	36.2
Total	4,486.3	4,583
Level 2 | Fair Value, Measurements, Recurring | Short term investments, trading at fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	4.2	5
Level 2 | Fair Value, Measurements, Recurring | Derivatives at fair value, assets | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives at fair value	10.8	14.6
Level 2 | Fair Value, Measurements, Recurring | Derivatives at fair value, assets | Interest Rate Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities at fair value	(49.5)
Level 2 | Fair Value, Measurements, Recurring | Liabilities under derivative contracts — foreign exchange contracts | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities at fair value	(7.2)	(15.1)
Level 2 | Available for sale financial assets | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	3,456.8	3,558.5
Level 2 | Available for sale financial assets | Fair Value, Measurements, Recurring | U.S. government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Level 2 | Available for sale financial assets | Fair Value, Measurements, Recurring | U.S. agency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	39.5	47.4
Level 2 | Available for sale financial assets | Fair Value, Measurements, Recurring | Municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	48.2	47.2
Level 2 | Available for sale financial assets | Fair Value, Measurements, Recurring | Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	2,162.7	2,206.2
Level 2 | Available for sale financial assets | Fair Value, Measurements, Recurring | Non-U.S. government-backed corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	98.3	93.2
Level 2 | Available for sale financial assets | Fair Value, Measurements, Recurring | Non-U.S. government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	137	134.6
Level 2 | Available for sale financial assets | Fair Value, Measurements, Recurring | Asset-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	16.1	17.3
Level 2 | Available for sale financial assets | Fair Value, Measurements, Recurring | Agency mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	955	1,012.6
Level 2 | Short-term investments | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	11.5	11.9
Level 2 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	1,021.6	971.9
Level 2 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | U.S. government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Level 2 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	3	2.7
Level 2 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	763.9	720.2
Level 2 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Non-U.S. government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	203.6	197.2
Level 2 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Asset-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	2.3	2.4
Level 2 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Agency mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	48.8	49.4
Level 2 | Real estate funds | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Level 3 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Catastrophe bonds trading, at fair value	0	0
Total	(5.9)	(4.6)
Level 3 | Fair Value, Measurements, Recurring | Short term investments, trading at fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Level 3 | Fair Value, Measurements, Recurring | Derivatives at fair value, assets | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives at fair value	0	0
Level 3 | Fair Value, Measurements, Recurring | Derivatives at fair value, assets | Interest Rate Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities at fair value	0
Level 3 | Fair Value, Measurements, Recurring | Liabilities under derivative contracts — foreign exchange contracts | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities at fair value	0	0
Level 3 | Available for sale financial assets | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Level 3 | Available for sale financial assets | Fair Value, Measurements, Recurring | U.S. government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Level 3 | Available for sale financial assets | Fair Value, Measurements, Recurring | U.S. agency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Level 3 | Available for sale financial assets | Fair Value, Measurements, Recurring | Municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Level 3 | Available for sale financial assets | Fair Value, Measurements, Recurring | Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Level 3 | Available for sale financial assets | Fair Value, Measurements, Recurring | Non-U.S. government-backed corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Level 3 | Available for sale financial assets | Fair Value, Measurements, Recurring | Non-U.S. government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Level 3 | Available for sale financial assets | Fair Value, Measurements, Recurring | Asset-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Level 3 | Available for sale financial assets | Fair Value, Measurements, Recurring | Agency mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Level 3 | Short-term investments | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Level 3 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Level 3 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | U.S. government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Level 3 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Level 3 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Level 3 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Non-U.S. government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Level 3 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Asset-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Level 3 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Agency mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Level 3 | Real estate funds | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0	0
Accrued expenses and other payables | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan notes issued by variable interest entities, at fair value	(5.9)	(4.6)
Accrued expenses and other payables | Level 1 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan notes issued by variable interest entities, at fair value	0	0
Accrued expenses and other payables | Level 2 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan notes issued by variable interest entities, at fair value	0	0
Accrued expenses and other payables | Level 3 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan notes issued by variable interest entities, at fair value	$ (5.9)	$ (4.6)

Fair Value Measurements - Recon

Fair Value Measurements - Reconciliation of Liabilities Using Level 3 Inputs (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Accrued expenses (current liabilities)	$ 7.3	$ 9.5
Level 3 | Fair Value, Measurements, Recurring | Silverton 2016
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		86.6	$ 86.6
Distributed to third party		(45.8)
Total change in fair value included in the statement of operations		(1)
Ending balance		39.8
Level 3 | Fair Value, Measurements, Recurring | Silverton 2017
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	4.6
Distributed to third party	(0.2)
Total change in fair value included in the statement of operations	1.5
Ending balance	5.9		$ 4.6
Third party
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Accrued expenses (current liabilities)	$ 5.9	$ 7.6

Fair Value Measurements - Prici

Fair Value Measurements - Pricing Sources Used in Pricing Fixed Income Investments (Details)	Mar. 31, 2019	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Index providers	84.00%	84.00%
Pricing services	14.00%	13.00%
Broker-dealers	2.00%	3.00%
Total	100.00%	100.00%

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Securities Priced Using Pricing Information from Index Providers (Details) - Fixed income maturities - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Fair Value [Line Items]
Fair Market Value Determined using Prices from Index Providers	$ 5,339.9	$ 5,372.6
% of Total Fair Value by Security Type	84.00%	84.00%
U.S. government
Fair Value [Line Items]
Fair Market Value Determined using Prices from Index Providers	$ 1,577.9	$ 1,551.9
% of Total Fair Value by Security Type	100.00%	100.00%
U.S. agency
Fair Value [Line Items]
Fair Market Value Determined using Prices from Index Providers	$ 38.3	$ 45.7
% of Total Fair Value by Security Type	97.00%	96.00%
Municipal
Fair Value [Line Items]
Fair Market Value Determined using Prices from Index Providers	$ 15.5	$ 14.7
% of Total Fair Value by Security Type	30.00%	30.00%
Corporate
Fair Value [Line Items]
Fair Market Value Determined using Prices from Index Providers	$ 2,755.9	$ 2,775.7
% of Total Fair Value by Security Type	94.00%	95.00%
Non-U.S. government-backed corporate
Fair Value [Line Items]
Fair Market Value Determined using Prices from Index Providers	$ 44.1	$ 43.3
% of Total Fair Value by Security Type	45.00%	47.00%
Non-U.S. government
Fair Value [Line Items]
Fair Market Value Determined using Prices from Index Providers	$ 368.2	$ 366.1
% of Total Fair Value by Security Type	60.00%	56.00%
Asset-backed
Fair Value [Line Items]
Fair Market Value Determined using Prices from Index Providers	$ 7.8	$ 7.7
% of Total Fair Value by Security Type	42.00%	39.00%
Agency mortgage-backed
Fair Value [Line Items]
Fair Market Value Determined using Prices from Index Providers	$ 532.2	$ 567.5
% of Total Fair Value by Security Type	53.00%	53.00%

Fair Value Measurements - Loan

Fair Value Measurements - Loan Notes Issued by Variable Interest Entities (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gross written premiums	$ 1,013.8	$ 1,116.8
Maximum | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gross written premiums	61.1		$ 61.1
Reserve for losses	61.9		61.9
Loan notes held by third parties	325		325
Minimum | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gross written premiums	50.1		50.1
Reserve for losses	4.2		4.2
Loan notes held by third parties	325		325
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	6,662		6,667.2
Fair Value, Measurements, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	(5.9)		(4.6)
Fair Value, Measurements, Recurring | Level 3 | Silverton 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total			4.6
Amount of Level 3 liabilities settled		45.8
Total change in fair value included in the statement of operations		$ (1)
Fair Value, Measurements, Recurring | Level 3 | Silverton 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	5.9
Amount of Level 3 liabilities settled	0.2
Total change in fair value included in the statement of operations	1.5
Accrued expenses and other payables | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan notes held by third parties	5.9		4.6
Accrued expenses and other payables | Fair Value, Measurements, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan notes held by third parties	$ 5.9		$ 4.6
Measurement Input, Expected Term | Maximum | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contract period	365 days		365 days

Fair Value Measurements - Narra

Fair Value Measurements - Narrative (Details) $ in Millions	3 Months Ended					12 Months Ended
	Mar. 31, 2019USD ($)quote / Investment	Mar. 31, 2018USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2018USD ($)quote / Investment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Quotes per fixed income investment | quote / Investment	2.2					2
Silverton 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes Issued					$ 85
Silverton 2015, Third-party Funded
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes Issued					$ 70
Silverton 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes Issued				$ 125
Silverton 2016, Third-party Funded
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes Issued				$ 100
Silverton 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes Issued			$ 130
Silverton 2017, Third-party Funded
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes Issued			$ 105
Fair Value, Measurements, Recurring | Level 3 | Silverton
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Repayments of debt						$ 115.6
Fair Value, Measurements, Recurring | Level 3 | Silverton 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amount of Level 3 liabilities settled		$ 45.8
Fair Value, Measurements, Recurring | Level 3 | Silverton 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amount of Level 3 liabilities settled	$ 0.2

Reinsurance - Narrative (Detail

Reinsurance - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Concentration Risk [Line Items]
Plus reinsurance recoverable on unpaid losses at period end	$ 2,122.9	$ 2,077.6	$ 1,611.3	$ 1,515.2
Reinsurance recoverables, uncollateralized	$ 1,642	$ 1,497.8
AM Best, A Rating | Standard & Poor's, A Plus Rating | Lloyd's
Concentration Risk [Line Items]
Concentration Risk, Percentage	9.50%	10.20%
AM Best, A Plus Rating | Standard & Poor's, AA- Rating | Munich Re
Concentration Risk [Line Items]
Concentration Risk, Percentage	16.10%	15.70%
AM Best, A Plus Rating | Standard & Poor's, A Plus Rating | Everest
Concentration Risk [Line Items]
Concentration Risk, Percentage	10.00%	10.20%

Derivative Contracts - Fair Val

Derivative Contracts - Fair Value of Derivative Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Derivatives at fair value	$ 10.8	$ 14.6
Foreign Exchange Contracts | Not Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Derivative notional amount	1,274.1	1,257.3
Cash collateral provided	2.3	2.3
Foreign Exchange Contracts | Not Designated as Hedging Instruments | Derivatives at Fair Value
Derivatives, Fair Value [Line Items]
Derivative notional amount	667.6	496.5
Foreign Exchange Contracts | Not Designated as Hedging Instruments | Liabilities under Derivative Contracts
Derivatives, Fair Value [Line Items]
Liability notional amount	606.5	760.8
Foreign Exchange Contracts | Designated as Hedging Instrument | Derivatives at Fair Value
Derivatives, Fair Value [Line Items]
Derivative notional amount	70.8	0
Foreign Exchange Contracts | Designated as Hedging Instrument | Liabilities under Derivative Contracts
Derivatives, Fair Value [Line Items]
Derivative notional amount	0	94.3
Interest Rate Swap | Not Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Initial and margin posted	109.1	0
Interest Rate Swap | Not Designated as Hedging Instruments | Liabilities under Derivative Contracts
Derivatives, Fair Value [Line Items]
Liability notional amount	3,318	0
Level 2 | Fair Value, Measurements, Recurring | Foreign Exchange Contracts | Not Designated as Hedging Instruments | Derivatives at Fair Value
Derivatives, Fair Value [Line Items]
Derivatives at fair value	8.9	14.6
Level 2 | Fair Value, Measurements, Recurring | Foreign Exchange Contracts | Not Designated as Hedging Instruments | Liabilities under Derivative Contracts
Derivatives, Fair Value [Line Items]
Liabilities at fair value	(7.2)	(13.9)
Level 2 | Fair Value, Measurements, Recurring | Foreign Exchange Contracts | Designated as Hedging Instrument | Derivatives at Fair Value
Derivatives, Fair Value [Line Items]
Derivatives at fair value	1.9	0
Level 2 | Fair Value, Measurements, Recurring | Foreign Exchange Contracts | Designated as Hedging Instrument | Liabilities under Derivative Contracts
Derivatives, Fair Value [Line Items]
Liabilities at fair value	0	(1.2)
Level 2 | Fair Value, Measurements, Recurring | Interest Rate Swap | Not Designated as Hedging Instruments | Liabilities under Derivative Contracts
Derivatives, Fair Value [Line Items]
Liabilities at fair value	$ (49.5)	$ 0

Derivative Contracts - Gain_(Lo

Derivative Contracts - Gain/(Loss) Recognized in Income on Derivative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Not Designated as Hedging Instruments | Foreign Exchange Contracts | Change in Fair Value of Derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	$ (3.1)	$ 23.5
Not Designated as Hedging Instruments | Interest Rate Swap | Change in Fair Value of Derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	(50.2)	0
Designated as Hedging Instrument | Foreign Exchange Contracts | General and Administrative Expense
Derivative Instruments, Gain (Loss) [Line Items]
Foreign exchange contract settlement	0.4	1.7
Designated as Hedging Instrument | Foreign Exchange Contracts | Net change from current period hedged transactions
Derivative Instruments, Gain (Loss) [Line Items]
Foreign exchange contracts, net change	$ 1.7	$ 0.9

Derivative Contracts - Narrativ

Derivative Contracts - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Foreign Exchange Contracts | Not Designated as Hedging Instruments
Derivative Instruments, Gain (Loss) [Line Items]
Derivative notional amount	$ 1,274.1		$ 1,257.3
Foreign Exchange Contracts | Not Designated as Hedging Instruments | Change in Fair Value of Derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	(3.1)	$ 23.5
Foreign Exchange Contracts | Designated as Hedging Instrument | General and Administrative Expense
Derivative Instruments, Gain (Loss) [Line Items]
Foreign exchange contract settlement	0.4	1.7
Foreign Exchange Contracts | Designated as Hedging Instrument | Net change from current period hedged transactions
Derivative Instruments, Gain (Loss) [Line Items]
Net unrealized gain (loss)	1.7	0.9
Foreign Exchange Contracts | Derivatives at Fair Value | Not Designated as Hedging Instruments
Derivative Instruments, Gain (Loss) [Line Items]
Derivative notional amount	667.6		496.5
Foreign Exchange Contracts | Derivatives at Fair Value | Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Derivative notional amount	70.8		0
Foreign Exchange Contracts | Liabilities under Derivative Contracts | Not Designated as Hedging Instruments
Derivative Instruments, Gain (Loss) [Line Items]
Liability notional amount	606.5		760.8
Foreign Exchange Contracts | Liabilities under Derivative Contracts | Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Derivative notional amount	0		94.3
Interest Rate Swap | Not Designated as Hedging Instruments
Derivative Instruments, Gain (Loss) [Line Items]
Initial and margin posted	109.1		0
Interest Rate Swap | Not Designated as Hedging Instruments | Change in Fair Value of Derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	(50.2)	$ 0
Interest Rate Swap | Liabilities under Derivative Contracts | Not Designated as Hedging Instruments
Derivative Instruments, Gain (Loss) [Line Items]
Liability notional amount	$ 3,318		$ 0

Deferred Policy Acquisition C_3

Deferred Policy Acquisition Costs - Reconciliation of Beginning and Ending Deferred Policy Acquisition Costs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance at the beginning of the period	$ 248.5	$ 294.3
Acquisition costs deferred	128.1	116.4
Amortization of deferred policy acquisition costs	(88.2)	(90.8)
Balance at the end of the period	$ 288.4	$ 319.9

Reserves for Losses and Loss _3

Reserves for Losses and Loss Adjustment Expenses - Reconciliation of Beginning and Ending Consolidated Loss and Loss Adjustment Expenses ("LAE") Reserves (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Provision for losses and LAE at the start of the year	$ 7,074.2	$ 6,749.5	$ 6,749.5
Net loss and LAE at the start of the year	4,996.6	5,234.3	5,234.3
Provision for losses and LAE for claims incurred:
Current year	304.2	347.9	1,684.1
Prior years	7.6	(37.7)	(111.1)
Total incurred	311.8	310.2	1,573
Losses and LAE payments for claims incurred:
Current year	(7.1)	(7.4)	(285.7)
Prior years	(474.8)	(483.7)	(1,441)
Total paid	(481.9)	(491.1)	(1,726.7)
Foreign exchange losses/(gains)	50.9	14.7	(84)
Net losses and LAE reserves at period end	4,877.4	5,068.1	4,996.6
Plus reinsurance recoverable on unpaid losses at period end	2,122.9	1,611.3	2,077.6	$ 1,515.2
Provision for losses and LAE at the end of the relevant period	$ 7,000.3	$ 6,679.4	$ 7,074.2

Reserves for Losses and Loss _4

Reserves for Losses and Loss Adjustment Expenses - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Insurance [Abstract]
Reserve releases	$ 7.6	$ (37.7)	$ (111.1)

Capital Structure - Summary of

Capital Structure - Summary of Authorized and Issued Share Capital (Details) - USD ($)	Mar. 31, 2019		Dec. 31, 2018	Sep. 20, 2016
Class of Stock [Line Items]
Ordinary shares, par value (in usd per share)	$ 0.01	[1]	$ 0.0015144558
Authorized share capital:
Number of ordinary shares (in shares)	70,000,000		969,629,030
Number of non-voting shares (in shares)	0		6,787,880
Number of preference shares (in shares)	30,000,000		100,000,000
Ordinary Shares $0.01 per share (2018: 0.15144558¢ per share)	$ 700,000		$ 1,469,000
Non-Voting Shares 0.15144558¢ per share	0		10,000
Preference Shares 0.15144558¢ per share	45,000		152,000
Total authorized share capital	$ 745,434		$ 1,631,000
Issued share capital:
Ordinary shares, issued (in shares)	60,395,839		59,743,156
Issued ordinary shares of $0.01 per share (2018: 0.15144558¢ per share)	$ 604,000		$ 90,000
Total issued share capital	$ 636,000		$ 122,000
Non Voting Shares Par Or Stated Value Per Share	$ 0		$ 0.0015144558
Preference shares, par value (in usd per share)	0.0015144558		0.0015144558
Preferred shares, liquidation preference (in USD per share)	$ 25		$ 25
5.95% preference shares
Issued share capital:
Preference shares, issued (in shares)	11,000,000		11,000,000
Issued preference shares of 0.15144558¢ each with a liquidation preference	$ 17,000		$ 17,000
Preference shares, par value (in usd per share)	$ 0.0015144558		$ 0.0015144558
Preferred shares, liquidation preference (in USD per share)	$ 25		$ 25
Preferred Stock Dividends Rate Percentage	5.95%		5.95%
5.625% preference shares
Issued share capital:
Preference shares, issued (in shares)	10,000,000		10,000,000	10,000,000
Issued preference shares of 0.15144558¢ each with a liquidation preference	$ 15,000		$ 15,000
Preference shares, par value (in usd per share)	$ 0.0015144558		$ 0.0015144558
Preferred shares, liquidation preference (in USD per share)	$ 25		$ 25
Preferred Stock Dividends Rate Percentage	5.625%		5.625%
[1]	On February 15, 2019, the Company completed its previously announced merger (the “Merger”) with Highlands Merger Sub, Ltd. (“Merger Sub”), a wholly owned subsidiary of Highlands Holdings, Ltd. (“Parent”). As a result of the Merger, a change in control of the Company occurred and the Company is now a wholly owned subsidiary of Parent. At the effective time of the Merger, each of the Company’s issued and outstanding ordinary shares (other than ordinary shares owned by the Company as treasury shares, owned by any subsidiary of the Company or owned by Parent, Merger Sub or any subsidiary thereof) was automatically canceled and converted into the right to receive $42.75 in cash, without interest and less any required tax withholdings. The ordinary shares of the Company ceased trading on the New York Stock Exchange prior to the opening of trading on February 15, 2019. Therefore, earnings per share data is no longer considered meaningful for both the current reporting period and for the comparative period and has been excluded. For more information on the Merger, refer to Note 1 of these unaudited condensed consolidated financial statements.

Capital Structure - Summary o_2

Capital Structure - Summary of Ordinary Shares (Details)	3 Months Ended
	Mar. 31, 2019shares
Ordinary Shares [Roll Forward]
Ordinary shares in issue as at December 31, 2018	59,743,156
Ordinary shares issued to employees under the 2013 share incentive plan and/or 2008 share purchase plan	144,269
Ordinary shares issued to non-employee directors	6,993
Ordinary shares canceled	59,894,418
Total ordinary shares of 0.015144558c per share in issue	0
Ordinary shares in issue as at March 31, 2019	60,395,839

Capital Structure - Narrative (

Capital Structure - Narrative (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2019		Dec. 31, 2018	Feb. 15, 2019
Class of Stock [Line Items]
Additional paid-in capital	$ 967,800,000		$ 967,500,000
Aggregate liquidation preferences	525,000,000		525,000,000
Issuance costs	13,100,000		13,100,000
Business acquisition, share price				$ 42.75
Authorized Share Capital	$ 745,434		$ 1,631,000
Number of ordinary shares (in shares)	70,000,000		969,629,030
Ordinary shares, par value (in usd per share)	$ 0.01	[1]	$ 0.0015144558
Ordinary shares, issued (in shares)	60,395,839		59,743,156
Number of preference shares (in shares)	30,000,000		100,000,000
[1]	On February 15, 2019, the Company completed its previously announced merger (the “Merger”) with Highlands Merger Sub, Ltd. (“Merger Sub”), a wholly owned subsidiary of Highlands Holdings, Ltd. (“Parent”). As a result of the Merger, a change in control of the Company occurred and the Company is now a wholly owned subsidiary of Parent. At the effective time of the Merger, each of the Company’s issued and outstanding ordinary shares (other than ordinary shares owned by the Company as treasury shares, owned by any subsidiary of the Company or owned by Parent, Merger Sub or any subsidiary thereof) was automatically canceled and converted into the right to receive $42.75 in cash, without interest and less any required tax withholdings. The ordinary shares of the Company ceased trading on the New York Stock Exchange prior to the opening of trading on February 15, 2019. Therefore, earnings per share data is no longer considered meaningful for both the current reporting period and for the comparative period and has been excluded. For more information on the Merger, refer to Note 1 of these unaudited condensed consolidated financial statements.

Share-Based Payments - Narrativ

Share-Based Payments - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2019	Feb. 15, 2019
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Business acquisition, share price		$ 42.75
Share-based compensation expense	$ 21.6
Offset settlement of accelerated vesting charge	$ 21.6

Intangible Assets and Goodwil_2

Intangible Assets and Goodwill - Summary of Changes in Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Finite and Indefinite Lived Intangible Assets [Roll Forward]
Amortization	$ (0.4)	$ (0.4)
Goodwill [Roll Forward]
Goodwill, Beginning of the period	3.9	3.9
Goodwill, Additions	0	0
Goodwill, End of the period	3.9	3.9
Intangible assets and goodwill, Beginning of the period	26.3	27.9
Intangible Assets and Goodwill, Acquired	0	0
Intangible assets and goodwill, End of the period	25.9	27.5
Trademark
Finite and Indefinite Lived Intangible Assets [Roll Forward]
Intangible Assets, Beginning of the period	2.5	2.9
Intangible Assets, Additions	0	0
Amortization	(0.1)	(0.1)
Intangible Assets, End of the period	2.4	2.8
Insurance Licenses
Finite and Indefinite Lived Intangible Assets [Roll Forward]
Intangible Assets, Beginning of the period	16.7	16.7
Intangible Assets, Additions	0	0
Amortization	0	0
Intangible Assets, End of the period	16.7	16.7
Agency Relationships
Finite and Indefinite Lived Intangible Assets [Roll Forward]
Intangible Assets, Beginning of the period	1.8	2.3
Intangible Assets, Additions	0	0
Amortization	(0.1)	(0.1)
Intangible Assets, End of the period	1.7	2.2
Non-compete Agreements
Finite and Indefinite Lived Intangible Assets [Roll Forward]
Intangible Assets, Beginning of the period	0.4	0.7
Intangible Assets, Additions	0	0
Amortization	(0.1)	(0.1)
Intangible Assets, End of the period	0.3	0.6
Contractual Rights
Finite and Indefinite Lived Intangible Assets [Roll Forward]
Intangible Assets, Beginning of the period	1	1.4
Intangible Assets, Additions	0	0
Amortization	(0.1)	(0.1)
Intangible Assets, End of the period	$ 0.9	$ 1.3

Intangible Assets and Goodwil_3

Intangible Assets and Goodwill - Narrative (Details) - USD ($) $ in Thousands	Dec. 18, 2017	Jan. 01, 2017	Oct. 31, 2016	Sep. 22, 2016	Apr. 05, 2005	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Sep. 18, 2018	Dec. 31, 2017
Finite And Indefinite Lived Intangible Assets By Major Class [Line Items]
Goodwill						$ 0	$ 0
Impairment charge								$ 3,400
Blue Waters
Finite And Indefinite Lived Intangible Assets By Major Class [Line Items]
Percentage of interests acquired			100.00%
Consideration transferred			$ 8,000
Residual assets			300
Total assets acquired, net			5,750
Goodwill			2,100
Agency Relationships
Finite And Indefinite Lived Intangible Assets By Major Class [Line Items]
Value of the asset						1,700	2,200	1,800		$ 2,300
Trademark
Finite And Indefinite Lived Intangible Assets By Major Class [Line Items]
Value of the asset						$ 2,400	2,800	2,500		2,900
Trademark | Blue Waters
Finite And Indefinite Lived Intangible Assets By Major Class [Line Items]
Value of the asset			1,500
Asset amortization period						5 years
Insurance Licenses
Finite And Indefinite Lived Intangible Assets By Major Class [Line Items]
Value of the asset						$ 16,700	16,700	16,700		16,700
Insurance Licenses | Blue Waters
Finite And Indefinite Lived Intangible Assets By Major Class [Line Items]
Value of trading licenses			50
Contractual Rights
Finite And Indefinite Lived Intangible Assets By Major Class [Line Items]
Value of the asset						$ 900	1,300	1,000		1,400
Customer Lists | Blue Waters
Finite And Indefinite Lived Intangible Assets By Major Class [Line Items]
Value of the asset			3,100
Asset amortization period						5 years
Non-compete Agreements
Finite And Indefinite Lived Intangible Assets By Major Class [Line Items]
Value of the asset						$ 300	$ 600	400		$ 700
Non-compete Agreements | Blue Waters
Finite And Indefinite Lived Intangible Assets By Major Class [Line Items]
Value of the asset			$ 1,000
Asset amortization period						5 years
Crop Re
Finite And Indefinite Lived Intangible Assets By Major Class [Line Items]
Equity method investment, ownership percentage	23.20%
Digital Re
Finite And Indefinite Lived Intangible Assets By Major Class [Line Items]
Equity method investment, ownership percentage		49.00%
Goodwill		$ 1,800
LSML | Insurance Licenses
Finite And Indefinite Lived Intangible Assets By Major Class [Line Items]
Value of the asset				$ 1,900
LSML | Contractual Rights
Finite And Indefinite Lived Intangible Assets By Major Class [Line Items]
Asset amortization period				5 years
Aspen U.K.
Finite And Indefinite Lived Intangible Assets By Major Class [Line Items]
Aggregate consideration for sale and purchase agreement					$ 1,600
Aspen U.K. | Trademark
Finite And Indefinite Lived Intangible Assets By Major Class [Line Items]
Value of the asset						$ 1,600		1,600
Aspen U.K. | Insurance Licenses
Finite And Indefinite Lived Intangible Assets By Major Class [Line Items]
Acquired licenses						2,100
AAIC, Aspen Specialty, AIUK | Insurance Licenses
Finite And Indefinite Lived Intangible Assets By Major Class [Line Items]
Value of the asset						16,600		$ 16,600
AAIC | Insurance Licenses
Finite And Indefinite Lived Intangible Assets By Major Class [Line Items]
Acquired licenses						10,000
Aspen Specialty | Insurance Licenses
Finite And Indefinite Lived Intangible Assets By Major Class [Line Items]
Acquired licenses						$ 4,500
Disposed of by Sale | AgriLogic
Finite And Indefinite Lived Intangible Assets By Major Class [Line Items]
Sale of goodwill	$ (20,600)
Disposed of by Sale | AgriLogic | Trademark
Finite And Indefinite Lived Intangible Assets By Major Class [Line Items]
Intangible assets (disposed)	(3,100)
Disposed of by Sale | AgriLogic | Customer Lists
Finite And Indefinite Lived Intangible Assets By Major Class [Line Items]
Intangible assets (disposed)	(21,800)
Disposed of by Sale | AgriLogic | Non-compete Agreements
Finite And Indefinite Lived Intangible Assets By Major Class [Line Items]
Intangible assets (disposed)	$ (900)
Disposed of by Sale | AgriLogic Consulting, LLC | Consulting Relationships
Finite And Indefinite Lived Intangible Assets By Major Class [Line Items]
Sale of interest of consulting business									60.00%

Operating Leases - Schedule of

Operating Leases - Schedule of Operating Lease Costs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Leases [Abstract]
Amortization of right-of-use operating lease assets	$ 3.3	$ 0
Interest on operating lease liabilities	1.2
Operating lease charge	$ 4.5	$ 0

Operating Leases - Schedule o_2

Operating Leases - Schedule of Operating Lease Liability, Maturity (Details) - USD ($) $ in Millions	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Leases [Abstract]
Liability, Payment, Remainder of fiscal year	$ 12.9
Liability, Payment, Next twelve months (2020)	14.2
Liability, Payments, Due year two (2021)	11.8
Liability, Payments, Due year three (2022)	9.4
Liability, Payments, Due year four (2023)	8.9
Liability, Payments, Due after year five	64.5
Total minimum lease payments	121.7
Less imputed interest	(27.8)
Operating lease liabilities	$ 93.9	$ 93.6	$ 0

Operating Leases - Summary of O

Operating Leases - Summary of Operating Leases Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Leases [Abstract]
Operating lease liabilities	$ (4.5)	$ 0
Reduction of right-of-use assets resulting from reductions to lease obligations	1.2
Asset obtained in exchange for operating lease liability	$ 3.1
Operating lease, weighted average remaining lease term (years)	10 years 6 months
Operating lease, weighted average discount rate (percent)	5.00%

Operating Leases - Narrative (D

Operating Leases - Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Leases [Abstract]
Right-of-use operating lease assets	$ 91.4		$ 0
Operating lease liabilities	$ 93.9	$ 93.6	$ 0

Commitments and Contingent Li_3

Commitments and Contingent Liabilities - Schedule of Company's Restricted Assets (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018	Dec. 20, 2017
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Restricted assets	$ 4,564.6	$ 4,419.2
Total as percent of investable assets(2)	58.50%	56.40%
Securities and cash as collateral secured letters of credit	$ 792.4	$ 771.1
Letters of credit / guarantees
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Restricted assets	792.4	771.1
Affiliated transactions
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Restricted assets	922.5	1,033.9
Third party
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Restricted assets	2,745.7	2,511.7
Limited Partner | Real estate funds
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Restricted assets	0	0	$ 100
Purchase Commitment | Limited Partner | Real estate funds
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Restricted assets	$ 104	$ 102.5

Commitments and Contingent Li_4

Commitments and Contingent Liabilities - Narrative (Details) $ / shares in Units, £ in Millions	Mar. 27, 2017USD ($)	Jun. 30, 2016	Mar. 31, 2019USD ($)	Mar. 31, 2019GBP (£)	Feb. 15, 2019$ / shares	Dec. 31, 2018USD ($)	Dec. 31, 2018GBP (£)	Sep. 19, 2018USD ($)	May 10, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 20, 2017USD ($)
Line of Credit Facility [Line Items]
Restricted assets			$ 4,564,600,000			$ 4,419,200,000
Other investments			104,000,000			102,500,000
Assets held by insurance regulators			516,200,000			503,200,000
Minimum capital required | £				£ 0.4			£ 0.4
Maximum borrowing capacity	$ 200,000,000
Line Of Credit Facility Increasable Capacity	$ 100,000,000
Long-term Line of Credit			0
Line Of Credit Facility Tangible Net Worth Restrictions Minimum			$ 2,323,100,000
Line Of Credit Facility Tangible Net Worth Net Income Restriction			25.00%
Line Of Credit Facility Tangible Net Worth Cash Proceeds From Issuance Of Capital Stock Restriction			25.00%
Percentage Of Consolidated Leverage Ratio Permitted			35.00%
Business acquisition, share price | $ / shares					$ 42.75
Letter of Credit
Line of Credit Facility [Line Items]
Restricted assets			$ 792,400,000			771,100,000
Citi Europe | Letter of Credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity										$ 550,000,000
Outstanding letters of credit			466,400,000			444,200,000
National Australia Bank Limited | Letter of Credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity										$ 100,000,000
LIBOR | Citi Europe | Letter of Credit
Line of Credit Facility [Line Items]
Variable rate basis spread		1.00%
Limited Partner | Real estate funds
Line of Credit Facility [Line Items]
Restricted assets			$ 0			$ 0					$ 100,000,000
Other investments								$ 13,800,000	$ 86,200,000

Related Party Transactions - Na

Related Party Transactions - Narrative (Details) $ in Millions	Feb. 15, 2019	Mar. 31, 2019USD ($)
Maximum
Related Party Transaction [Line Items]
Percentage of consolidated group's net income due to Apollo Management		1.00%
Fee due to Apollo Management		$ 5
Affiliated transactions
Related Party Transaction [Line Items]
Initial term	8 years
Automatic twelve month extension	12 months
Automatic twelve month extension, eight years	8 years
Automatic twelve month extension, nine years	9 years
Term extension period	30 days
Beneficial Owner | Maximum
Related Party Transaction [Line Items]
Ownership percentage	0.90

Subsequent Events - Narrative (

Subsequent Events - Narrative (Details) - Maximum - Subsequent Event	Apr. 30, 2019
Subsequent Event [Line Items]
Investment company advisory service, mark-up, percent	25.00%
Annual fee cap, percent	15.00%