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Investments in Unconsolidated Affiliates (Symetra Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions |  | 3 Months Ended | 6 Months Ended | 10 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Feb. 01, 2016 | Dec. 31, 2015 | Jun. 30, 2013 | Nov. 05, 2015 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013 | Jun. 20, 2013 | Dec. 31, 2012 | Dec. 31, 2011
Investments in unconsolidated affiliates |  |  |  |  |  |  |  |  |  |
Trading Securities, Change in Unrealized Holding Gain (Loss) |  |  |  |  | $ 152.9 | $ (79.3) | $ 40.3 |  |  |
Trading Securities Unrealized Holding Gain (Loss) on Investments after Tax |  |  |  |  | 140.6 | (69.4) | 43.6 |  |  |
After tax amortization through equity in net unrealized losses |  |  |  |  | (36.3) | 75.3 | (98.1) |  |  |
Sales of common equity securities |  |  |  |  | $ 461.4 | $ 609.8 | 435.0 |  |  |
Common shares, par value per share (in dollars per share) |  | $ 1.00 |  |  | $ 1.00 | $ 1.00 |  |  |  |
Symetra |  |  |  |  |  |  |  |  |  |
Investments in unconsolidated affiliates |  |  |  |  |  |  |  |  |  |
Trading Securities, Change in Unrealized Holding Gain (Loss) |  | $ 258.8 |  |  |  |  |  |  |  |
Trading Securities Unrealized Holding Gain (Loss) on Investments after Tax |  | $ 241.1 |  |  |  |  |  |  |  |
Stock Dividends, Shares |  |  |  |  | 513,500 |  |  |  |  |
Shares of symetra financial corporation owned (in shares) |  |  |  | 20,562,379 |  | 20,048,879 |  |  |  |
Ownership interest (as a percent) |  |  |  | 17.70% |  | 17.31% |  |  |  |
Dividends received |  |  |  | $ (16.9) |  | $ (34.1) | $ (6.4) |  |  |
Investments in unconsolidated affiliates on conversion of warrants |  |  |  |  |  |  | 9,490,000 | 2,650,000 | 9,490,000 |
Gain (Loss) on Warrants |  |  |  |  |  |  | $ 10.8 |  |  |
Fair value of investment |  |  |  |  |  |  |  |  |  | $ 261.0
Estimated fair value of investment per share |  |  |  |  |  |  |  |  |  | $ 15
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity |  |  |  | 159.9 |  | 170.4 |  |  |  |
Term of amortization (in years) |  |  |  |  | 30 years |  |  |  |  |
Common Stock | Symetra |  |  |  |  |  |  |  |  |  |
Investments in unconsolidated affiliates |  |  |  |  |  |  |  |  |  |
Dividends received |  |  |  | $ (16.9) |  | (34.1) | (6.4) |  |  |
Per share price, class of warrant (in dollars per share) |  |  |  | $ 31.67 |  |  |  |  |  |
Gain (Loss) on Warrants |  |  |  |  |  |  | 0.0 |  |  |
Warrants |  |  |  |  |  |  |  |  |  |
Investments in unconsolidated affiliates |  |  |  |  |  |  |  |  |  |
Gain (Loss) on Warrants |  |  | $ 10.8 |  |  |  |  |  |  |
Warrants | Symetra |  |  |  |  |  |  |  |  |  |
Investments in unconsolidated affiliates |  |  |  |  |  |  |  |  |  |
Dividends received |  |  |  | $ 0.0 |  | 0.0 | $ 0.0 |  |  |
Per share price, class of warrant (in dollars per share) |  |  |  |  |  |  | $ 11.49 |  |  |
Gain (Loss) on Warrants |  |  |  |  |  |  | $ 10.8 |  |  |
Cash dividends received on warrants |  |  | $ 1.5 |  |  |  |  |  |  |
equity in earnings of unconsolidated affiliates [Member] | Symetra |  |  |  |  |  |  |  |  |  |
Investments in unconsolidated affiliates |  |  |  |  |  |  |  |  |  |
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity |  |  |  | 32.6 |  | 36.4 |  |  |  |
After tax amortization through equity in earnings |  |  |  | 2.2 |  | 2.8 | 2.7 |  |  |
Net unrealized gains (losses) of unconsolidated affiliates [Member] | Symetra |  |  |  |  |  |  |  |  |  |
Investments in unconsolidated affiliates |  |  |  |  |  |  |  |  |  |
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity |  |  |  | 127.3 |  | 134.0 |  |  |  |
After tax amortization through equity in net unrealized losses |  |  |  | $ 8.9 |  | $ 11.7 | $ 10.8 |  |  |
Subsequent Event [Member] | Symetra |  |  |  |  |  |  |  |  |  |
Investments in unconsolidated affiliates |  |  |  |  |  |  |  |  |  |
Sales of common equity securities | $ 658.0 |  |  |  |  |  |  |  |  |
Common shares, par value per share (in dollars per share) | $ 32.00 |  |  |  |  |  |  |  |  |

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