Debt (Details)	12 Months Ended			12 Months Ended		0 Months Ended	1 Months Ended			12 Months Ended																														0 Months Ended	12 Months Ended	0 Months Ended				0 Months Ended		12 Months Ended
	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2010 Private Equity Partnership Structures I, LLC (PEPS I) USD ($)	Oct. 02, 2010 Hewitt Associates, Inc (Hewitt) USD ($)	Jul. 02, 2009 2005 Facility USD ($)	Oct. 31, 2010 Euro Facility	Dec. 31, 2012 Euro Facility USD ($)	Oct. 15, 2010 Euro Facility EUR (€)	Dec. 31, 2012 Term Loan Facility due 2013 USD ($)	Dec. 31, 2011 Term Loan Facility due 2013 USD ($)	Jun. 15, 2011 Term Loan Facility due 2013 USD ($)	Dec. 31, 2012 6.25% EUR 500 debt securities due July 2014 USD ($)	Dec. 31, 2011 6.25% EUR 500 debt securities due July 2014 USD ($)	Jul. 02, 2009 6.25% EUR 500 debt securities due July 2014 USD ($)	Jul. 02, 2009 6.25% EUR 500 debt securities due July 2014 EUR (€)	Dec. 31, 2012 5.00% Senior notes due September 2020 USD ($)	Dec. 31, 2011 5.00% Senior notes due September 2020 USD ($)	Sep. 07, 2010 5.00% Senior notes due September 2020 USD ($)	Dec. 31, 2012 3.50% senior notes due September 2015 USD ($)	Dec. 31, 2011 3.50% senior notes due September 2015 USD ($)	Sep. 07, 2010 3.50% senior notes due September 2015 USD ($)	Dec. 31, 2012 8.205% Junior subordinated deferrable interest debentures due January 2027 USD ($)	Dec. 31, 2011 8.205% Junior subordinated deferrable interest debentures due January 2027 USD ($)	Dec. 31, 2012 3.125% Senior notes due May 2016 USD ($)	Dec. 31, 2011 3.125% Senior notes due May 2016 USD ($)	May 24, 2011 3.125% Senior notes due May 2016 USD ($)	Dec. 31, 2012 4.768% CAD 375 debt securities due March 2018 USD ($)	Dec. 31, 2011 4.768% CAD 375 debt securities due March 2018 USD ($)	Mar. 08, 2011 4.768% CAD 375 debt securities due March 2018 CAD	Dec. 31, 2012 6.25% Senior notes due September 2040 USD ($)	Dec. 31, 2011 6.25% Senior notes due September 2040 USD ($)	Sep. 07, 2010 6.25% Senior notes due September 2040 USD ($)	Dec. 31, 2012 7.375% Debt securities due December 2012	Dec. 31, 2011 7.375% Debt securities due December 2012 USD ($)	Dec. 31, 2012 4.25% senior notes due December 2042 USD ($)	Dec. 12, 2012 4.25% senior notes due December 2042 USD ($)	Dec. 31, 2012 Other USD ($)	Dec. 31, 2011 Other USD ($)	Aug. 13, 2010 2010 Term loan credit facility USD ($)	Dec. 31, 2011 2010 Term loan credit facility USD ($)	Oct. 02, 2010 2010 Term loan credit facility Hewitt Associates, Inc (Hewitt) USD ($)	Apr. 12, 2011 5.05% CAD 375 debt securities due April 2011 CAD	Sep. 07, 2010 Notes USD ($)	Oct. 02, 2010 Senior Notes Hewitt Associates, Inc (Hewitt) USD ($)	Sep. 15, 2010 Bridge Loan Facility USD ($)	Aug. 13, 2010 Bridge Loan Facility USD ($)	Dec. 31, 2012 Commercial paper USD ($)	Dec. 31, 2011 Commercial paper USD ($)	Dec. 31, 2012 Revolving Credit Agreement Federal Funds rate	Dec. 31, 2012 Revolving Credit Agreement Prime rate	Dec. 31, 2012 Revolving Credit Agreement One month Eurodollar rate
Debt Instrument
Debt face value												$ 450,000,000	$ 661,000,000			€ 500,000,000			$ 600,000,000			$ 600,000,000					$ 500,000,000			375,000,000			$ 300,000,000				$ 166,000,000
Interest rate on debt (as a percent)													6.25%		6.25%	6.25%	5.00%		5.00%	3.50%		3.50%	8.205%		3.125%		3.125%	4.768%			6.25%		6.25%	7.375%		4.25%	4.25%						5.05%
Total debt	4,492,000,000		4,165,000,000							383,000,000	428,000,000		661,000,000	653,000,000			598,000,000	598,000,000		598,000,000	597,000,000		521,000,000	687,000,000	500,000,000	500,000,000		377,000,000	368,000,000		297,000,000	297,000,000			225,000,000	107,000,000		123,000,000	139,000,000									50,000,000	50,000,000
Weighted average commercial paper outstanding																																																67,000,000	35,000,000
Weighted-average interest rates (as a percent)																																																0.41%	0.35%
Less short-term and current portion of long-term debt	337,000,000		452,000,000
Total long-term debt	4,155,000,000		3,713,000,000
Unamortized premium																																					59,000,000
New credit and loan facility								860,000,000	650,000,000																															1,000,000,000							1,500,000,000
Deferred financing cost amortization for Term Loan Credit Facility and Notes																																								26,000,000				12,000,000
Deferred financing costs expense																																														14,000,000
(Loss) gain on extinguishment of debt	19,000,000	8,000,000																																							19,000,000
Debt assumed on acquisition					346,000,000																																								299,000,000
Carrying value of debt related to hedging activities															11,000,000
Amount borrowed under five-year multi-currency foreign credit facility (""Euro credit facility"")																																										1,000,000,000
Commitment fees (in basis points)							0.35%
Debt repayment						677,000,000																																			1,000,000,000		375,000,000
Term of credit facility																																								3 years
Annualized interest rate including LIBOR (as a percent)										1.59%
Debt instrument base interest rate										LIBOR																														LIBOR										Federal fund effective rate	Prime rate	One month Eurodollar rate
Debt Instrument, Variable Rate (as a percent)										1.38%																														2.50%										0.50%		1.00%
Repurchase of debt held by PEPS I				$ 47,000,000