Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2012 Customer relationships	Dec. 31, 2012 Acquired software	Dec. 31, 2012 Cash and cash equivalents [Member]	Dec. 31, 2012 Short-term Investments [Member]	Dec. 31, 2012 Alternative funds	Dec. 31, 2012 Private investment funds	Dec. 31, 2012 Operating affiliates	Dec. 31, 2012 Investments In Common Stock Of Corporations [Member]	Dec. 31, 2012 Investments In Other Types Of Legal Structures [Member]	Dec. 31, 2012 Maximum	Dec. 31, 2012 Minimum	Dec. 31, 2011 Accounting Standards Update 2010-26 [Member]
Significant Accounting Policies [Line Items]
Deferred tax liability, cumulative adjustment effect													$ 7.0
Deferred acquisition costs, cumulative adjustment effect													21.0
Net assets, cumulative adjustment effect													$ 14.0
Time period for classification, as shown				90 days	1 year
Alternative investments, timelag for reporting						1 month	3 months	3 months
Threshold for signicant influence, percentage									20.00%	3.00%
Hedge effectiveness, percentage											125.00%	80.00%
Useful life of intangible assets		10 years	5 years
Options, useful life	10 years
Vesting period required											4 years	3 years