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Investments in Unconsolidated Affiliates (Symetra) (Details) (USD $) In Millions, except Share data, unless otherwise specified | 3 Months Ended | 12 Months Ended |  | 3 Months Ended |  | 3 Months Ended | 6 Months Ended |  |  | 12 Months Ended |  |  | 12 Months Ended
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Mar. 31, 2014 | Mar. 31, 2013 | Mar. 31, 2014 Symetra | Mar. 31, 2013 Symetra | Dec. 31, 2011 Symetra | Jun. 20, 2013 Symetra | Mar. 31, 2014 Common Stock Symetra | Mar. 31, 2013 Common Stock Symetra | Dec. 31, 2011 Common Stock Symetra | Mar. 31, 2014 Warrants Symetra | Mar. 31, 2013 Warrants Symetra | Jun. 20, 2013 Symetra Common Stock | Mar. 31, 2014 equity in earnings of unconsolidated affiliates [Member] Symetra | Jun. 20, 2013 equity in earnings of unconsolidated affiliates [Member] Symetra | Dec. 31, 2011 equity in earnings of unconsolidated affiliates [Member] Common Stock Symetra | Mar. 31, 2014 Net unrealized gains (losses) of unconsolidated affiliates [Member] Symetra | Jun. 20, 2013 Net unrealized gains (losses) of unconsolidated affiliates [Member] Symetra | Dec. 31, 2011 Net unrealized gains (losses) of unconsolidated affiliates [Member] Common Stock Symetra
Investments in unconsolidated affiliates |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares of Symetra Financial Corporation owned (in shares) |  |  | 20,050,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) |  |  | 17.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investments In Unconsolidated Affiliates On Conversion Of Warrants |  |  |  |  |  | 9,490,000 |  |  |  |  |  |  |  |  |  |  |  |
Common shares received from exercised warrants |  |  |  |  |  | 2,650,000 |  |  |  |  |  |  |  |  |  |  |  |
Stock Repurchased and Retired During Period, Shares |  |  |  |  |  |  |  |  |  |  |  | 6,600,000 |  |  |  |  |  |
Average price per share | $ 586.00 | $ 564.00 |  |  |  |  |  |  |  |  |  | $ 13.44 |  |  |  |  |  |
Unamortized basis difference |  |  |  |  |  | $ 19.3 |  |  |  |  |  |  |  | $ 0.4 |  |  | $ 18.9 |
Fair value of investment |  |  |  |  |  |  |  |  | 261.0 |  |  |  |  |  |  |  |  |
Estimated fair value of investment per share |  |  |  |  |  |  |  |  | $ 15 |  |  |  |  |  |  |  |  |
Other than Temporary Impairment Losses, Investments |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 45.9 |  |  | 136.6
Term of amortization (in years) |  |  |  |  | 30 years |  |  |  |  |  |  |  |  |  |  |  |  |
Weight Average Years Remaining |  |  | 29 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
After tax amortization through equity in earnings |  |  | 0.7 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
After tax amortization through equity in net unrealized losses |  |  | 2.9 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity |  |  | 183.3 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Pre-tax unamortized basis difference |  |  |  |  |  |  |  |  |  |  |  |  | 39.0 |  |  | 144.3 |  |
Expected life (in years) |  |  |  |  |  |  |  |  |  |  | 1 year 1 month 90 days |  |  |  |  |  |  |
Class of warrant or right fair value assumptions per strike price |  |  |  |  |  |  |  |  |  |  | 11.49 |  |  |  |  |  |  |
Proceeds from Equity Method Investment, Dividends or Distributions |  |  | 2.0 | 1.4 |  |  | 2.0 | 1.4 |  | 0 | 0 |  |  |  |  |  |  |
Proceeds from Dividends Received |  |  |  |  |  |  |  |  |  |  | $ 0.8 |  |  |  |  |  |  |
Fair Value Assumptions, Risk Free Interest Rate |  |  |  |  |  |  |  |  |  |  | 0.17% |  |  |  |  |  |  |
Fair Value Assumptions, Expected Volatility Rate |  |  |  |  |  |  |  |  |  |  | 29.10% |  |  |  |  |  |  |
Share Price |  |  |  |  |  |  | $ 19.82 |  |  |  | $ 13.41 |  |  |  |  |  |  |

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