Guarantee of Registered Securities (Narrative) (Details)	Jun. 30, 2016	Mar. 01, 2016
Aon plc [Member]
Condensed Financial Statements, Captions [Line Items]
Parent company's percentage ownership of guarantors	100.00%
5.00% Senior notes due September 2020 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	5.00%
8.205% Junior subordinated deferrable interest debentures due January 2027 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	8.205%
6.25% Senior notes due September 2040 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	6.25%
4.250% Senior notes due 2042 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	4.25%
4.45% notes due 2043 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	4.45%
4.00% notes due 2023 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	4.00%
2.875% notes due 2026 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	2.875%
3.50% Notes due June 2024 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	3.50%
4.60% notes due May 2044 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	4.60%
4.75% Notes Due May 2045 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	4.75%
3.50% notes due 2024 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	3.50%
4.60% notes due 2044 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	4.60%
4.75% Notes Due 2045 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	4.75%
Two Point Eight Zero Percent Senior Notes Due Twenty Twenty One [Member] | Senior Notes [Member]
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	2.80%
3.875% due in December 2025 [Member] | Senior Notes [Member]
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	3.875%	3.875%