Summary of Significant Accounting Policies (Narratives) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of business segments	2
Uncollected Premiums and Claims, Net of Related Payables	$ 8,200,000,000	$ 9,100,000,000
Restricted Cash and Cash Equivalents	190,000,000
Indefinite-lived intangible assets	0	0
Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Investment securities	12,000,000	33,000,000	10,000,000
Trident III [Member] | Performance Fees [Member]
Schedule of Equity Method Investments [Line Items]
Deferred Revenue	38,000,000	63,000,000
Recognition of deferred performance fees	40,000,000
Trident II [Member] | Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Proceeds from Equity Method Investment, Dividends or Distributions	100,000,000
Trident II [Member] | Performance Fees [Member]
Schedule of Equity Method Investments [Line Items]
Recognition of deferred performance fees	15,000,000
Mercer Consulting Group [Member]
Schedule of Equity Method Investments [Line Items]
Assets in trusts or funds for management or trustee fee	16,000,000,000
Risk and Insurance Services Segment [Member]
Schedule of Equity Method Investments [Line Items]
Interest Income, Fiduciary Assets	27,000,000	39,000,000	47,000,000
Consulting Segment [Member]
Schedule of Equity Method Investments [Line Items]
Number of business groups	2
Interest Income, Fiduciary Assets	$ 5,000,000	$ 4,000,000	$ 4,000,000