Investing Activities Available-for-sale Securities Narrative (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014 security	Dec. 31, 2013 security
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses on below-investment-grade debt securities depressed of amortized cost (percent)	20.00%	20.00%
Unrealized losses on below-investment-grade debt securities depressed of amortized cost	$ 0.9	$ 1.0
Unrealized losses on below-investment-grade debt securities depressed of amortized cost for more than 12 month, amount	$ 0.6	$ 0.8
Unrealized losses on below-investment-grade debt securities depressed of amortized cost for more than 12 month (percent)	20.00%	20.00%
Available-for-sale securities, continuous unrealized loss position, 12 Months or longer, number of securities	127	79
Total available-for-sale debt securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position, 12 Months or longer, number of securities	123	79
Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position, 12 Months or longer, number of securities	4	0

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Unrealized losses on below-investment-grade debt securities depressed of amortized cost for more than 12 month, amount.

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Unrealized losses on below-investment-grade debt securities depressed of amortized cost for more than 12 month, percentage.

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Unrealized losses on below-investment-grade debt securities depressed of amortized cost, percentage.

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