Fair Value Measurement (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015 transfers	Mar. 31, 2014 transfers	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Percentage of portfolio of unadjusted fair values obtained	99.60%
Percentage of portfolio of specific unadjusted broker quotes obtained	0.40%
Transfers between Levels 1, 2, and 3 of the fair value hierarchy	0	0
Commercial Mortgage Backed Securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, fair value disclosure	46.1		$ 32.5
Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of knowledgeable outside security brokers consulted to determine fair value	1