Guarantee of Registered Securities Narrative (Details)	Dec. 31, 1997	Dec. 31, 2013 Aon plc [Member]	Dec. 31, 2013 3.50% senior notes due September 2015 [Member]	Sep. 07, 2010 3.50% senior notes due September 2015 [Member]	Dec. 31, 2013 Senior Notes 3point125 Percent Due 2016 [Member]	Dec. 31, 2013 5.00% Senior notes due September 2020 [Member]	Sep. 07, 2010 5.00% Senior notes due September 2020 [Member]	Dec. 31, 2013 Junior Subordinated Deferrable Interest Debentures 8point205 Percent Due 2027 [Member]	Dec. 31, 2013 6.25% Senior notes due September 2040 [Member]	Sep. 07, 2010 6.25% Senior notes due September 2040 [Member]	Dec. 31, 2013 Notes Due 2042 at 4.250 Percent [Member]	Dec. 31, 2013 Notes Due at 2043 at 4.45 Percent [Member]	Dec. 31, 2013 4.00% senior notes dues November 2023 [Member]	Nov. 21, 2013 4.00% senior notes dues November 2023 [Member]
Condensed Financial Statements, Captions [Line Items]
Parent company's percentage ownership of guarantors		100.00%
Debt interest rate	8.205%		3.50%	3.50%	3.125%	5.00%	5.00%	8.205%	6.25%	6.25%	4.25%	4.45%	4.00%	4.00%