Investments (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014 security	Dec. 31, 2013	Dec. 31, 2012
Schedule of Investments [Line Items]
Credit-related net investment impairment losses	$ 0	$ 0	$ 0.6
Number of pooled trust preferred securities	5
Annual prepayment rate	1.00%us-gaap_FairValueInputsPrepaymentRate	1.00%us-gaap_FairValueInputsPrepaymentRate
Annual prepayments maturity	100.00%	100.00%
Additional basis points	150.00%	150.00%
Carrying value of securities pledged	273	278
Maximum
Schedule of Investments [Line Items]
Equity ownership positions in the community bank holding companies	4.00%
Regional community bank stocks, percent of average trading volumes	0.10%
Pooled Bank Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Remaining book value	2.1
Pooled trust preferred securities, estimated fair value	$ 1.7

Additional basis points, annual defaults from banks.

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Number Of Pooled Trust Preferred Securities

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Amount of equity securities categorized neither as held-to-maturity nor as trading.

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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Rate at which loans or a loan portfolio are expected to prepay principal balances, used as an input to measure fair value.

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