The Company’s insurance subsidiaries are required to file annual statements with state regulatory authorities prepared on an accounting basis prescribed or permitted by such authorities (statutory basis), as codified by the National Association of Insurance Commissioners (“NAIC”). Permitted statutory accounting practices encompass all accounting practices that are not prescribed; such practices differ from state to state, may differ from company to company within a state, and may change in the future. The Company’s U.S. insurance subsidiaries did not have any permitted practices as of or for the years ended December 31, 2018, 2017, and 2016.

Statutory capital and surplus differs from shareholders’ equity reported in accordance with U.S. GAAP primarily because under the statutory basis of accounting, deferred acquisition costs are expensed when incurred and the recognition of deferred tax assets is based on different recoverability assumptions.

The following table provides statutory net income for the years ended December 31 and statutory capital and surplus as of December 31 for the periods indicated:

(in millions)	2018		2017		2016
Statutory Net Income
U.S. Insurance Subsidiaries	$	296.1	$	254.5	$	158.0
Statutory Capital and Surplus
U.S. Insurance Subsidiaries		2,172.5		2,077.1		2,173.4

The minimum statutory capital and surplus necessary to satisfy the Company’s regulatory requirements was $518.4 million, $500.7 million and $460.1 million, which equals the Authorized Control Level at December 31, 2018, 2017, and 2016, respectively. Beginning in 2017, the NAIC modified the RBC formula to require the inclusion of catastrophe risk. Accordingly, the Authorized Control Level for 2016 has been restated to reflect this change.