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Guarantee of Registered Securities (Narrative) (Details) | Mar. 31, 2018
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Aon plc |
Condensed Financial Statements, Captions [Line Items] |
Parent company's percentage ownership of guarantors | 100.00%
5.00% Senior notes due September 2020 |
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 |
Condensed Financial Statements, Captions [Line Items] |
Debt interest rate percentage (as a percent) | 8.205%
6.25% Senior notes due September 2040 |
Condensed Financial Statements, Captions [Line Items] |
Debt interest rate percentage (as a percent) | 6.25%
4.250% Senior notes due 2042 |
Condensed Financial Statements, Captions [Line Items] |
Debt interest rate percentage (as a percent) | 4.25%
4.45% notes due 2043 |
Condensed Financial Statements, Captions [Line Items] |
Debt interest rate percentage (as a percent) | 4.45%
4.00% notes due 2023 |
Condensed Financial Statements, Captions [Line Items] |
Debt interest rate percentage (as a percent) | 4.00%
2.875% notes due 2026 |
Condensed Financial Statements, Captions [Line Items] |
Debt interest rate percentage (as a percent) | 2.875%
3.50% Notes due June 2024 |
Condensed Financial Statements, Captions [Line Items] |
Debt interest rate percentage (as a percent) | 3.50%
4.60% notes due May 2044 |
Condensed Financial Statements, Captions [Line Items] |
Debt interest rate percentage (as a percent) | 4.60%
4.75% Notes Due May 2045 |
Condensed Financial Statements, Captions [Line Items] |
Debt interest rate percentage (as a percent) | 4.75%
2.80% Senior Notes Due 2021 |
Condensed Financial Statements, Captions [Line Items] |
Debt interest rate percentage (as a percent) | 2.80%
3.875% due in December 2025 |
Condensed Financial Statements, Captions [Line Items] |
Debt interest rate percentage (as a percent) | 3.875%

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- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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