Summary of Significant Accounting Principles and Practices (Details)	12 Months Ended				12 Months Ended
	Dec. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2012 GBP (£)	Dec. 31, 2012 Buildings	Dec. 31, 2012 Automobiles	Dec. 31, 2012 Minimum	Dec. 31, 2012 Minimum Software	Dec. 31, 2012 Minimum Furniture, fixtures and equipment	Dec. 31, 2012 Minimum Computer equipment	Dec. 31, 2012 Maximum	Dec. 31, 2012 Maximum Software	Dec. 31, 2012 Maximum Leasehold improvements	Dec. 31, 2012 Maximum Furniture, fixtures and equipment	Dec. 31, 2012 Maximum Computer equipment	Dec. 31, 2012 Weighted average
Revenue Recognition
Term of outsourcing contracts for benefit services							3 years				5 years
Term of outsourcing contracts for HR BPO services							5 years				10 years
Cash and Cash Equivalents
Operating funds in U.K.	$ 124,000,000	$ 120,000,000		£ 77,000,000
Cash and cash equivalents, restricted	76,000,000	71,000,000
Fiduciary Assets and Liabilities
Premium trust balances	4,000,000,000	4,200,000,000
Allowance for Doubtful Accounts
Allowance for doubtful accounts receivable	118,000,000	104,000,000
Fixed Assets
Fixed assets, original life, weighted-average					35 years	6 years		4 years	4 years	4 years		7 years	10 years	10 years	6 years
Goodwill and Intangible Assets
Useful life of finite-lived intangible assets							1 year				13 years					10 years
Foreign Currency
Effect of foreign exchange gains (losses) on the consolidated statements of income	(16,000,000)	10,000,000	(18,000,000)
Amount of Gain (Loss) Recognized in Income on Derivative	$ 3,000,000	$ (20,000,000)	$ (11,000,000)