Investments (Pledged Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
In favor of ceding companies, other counterparties, or government authorities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Restricted cash, cash equivalents and investments	$ 2,687.7	$ 2,748.9
Pledged as collateral for letter of credity facility
Schedule of Trading Securities and Other Trading Assets [Line Items]
Restricted cash, cash equivalents and investments	$ 587.6	$ 579.3

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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