Dividend Restrictions (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
New Hampshire's Statute [Member]
Maximum percentage of policyholder's surplus distributes as dividends and other distributions	10.00%
Dividends declared	$ 99.0	$ 75.0	$ 153.7
Additional dividends payable without prior approval from regulatory agency	58.8
Maximum dividends payable without prior approval of state regulators	157.8
Additional dividend approval date	April 2012
Michigan's Statute [Member]
Maximum percentage of policyholder's surplus distributes as dividends and other distributions	10.00%
Dividends declared	69.0	70.0	72.0
Maximum dividends payable without prior approval of state regulators	$ 70.2