Guarantee of Registered Securities Condensed Consolidating Statement of Financial Position (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
CURRENT ASSETS :
Cash and cash equivalents	$ 477	$ 291	$ 272	$ 346
Short-term investments	523	346
Receivables, net	2,896	3,101
Fiduciary assets	11,871	12,214
Intercompany receivables	0	0
Other current assets	563	430
Total Current Assets	16,330	16,382
Goodwill	8,997	8,943	8,770
Intangible assets, net	2,578	2,975
Fixed assets, net	791	820
Investments	132	165
Non-current deferred tax assets	193	285
Intercompany receivables	0	0
Other non-current assets	1,230	916
Investment in subsidiary	0	0
TOTAL ASSETS	30,251	30,486
CURRENT LIABILITIES
Fiduciary liabilities	11,871	12,214
Short-term debt and current portion of long-term debt	703	452
Accounts payable and accrued liabilities	1,931	1,853
Intercompany payables	0	0
Other current liabilities	906	831
Total Current Liabilities	15,411	15,350
Long-term debt	3,686	3,713
Non-current deferred tax liabilities	420	306
Pension, other post-retirement and other post-employment liabilities	1,607	2,276
Intercompany payables	0	0
Other non-current liabilities	932	1,036
TOTAL LIABILITIES	22,056	22,681
TOTAL AON SHAREHOLDERS’ EQUITY	8,145	7,762
Noncontrolling interests	50	43
TOTAL EQUITY	8,195	7,805	8,120	8,306
TOTAL LIABILITIES AND EQUITY	30,251	30,486
Aon plc [Member]
CURRENT ASSETS :
Cash and cash equivalents	0	131	0	0
Short-term investments	0	0
Receivables, net	0	5
Fiduciary assets	0	0
Intercompany receivables	186	0
Other current assets	0	7
Total Current Assets	186	143
Goodwill	0	0
Intangible assets, net	0	0
Fixed assets, net	0	0
Investments	0	0
Non-current deferred tax assets	140	117
Intercompany receivables	7,166	166
Other non-current assets	6	0
Investment in subsidiary	4,607	10,398
TOTAL ASSETS	12,105	10,824
CURRENT LIABILITIES
Fiduciary liabilities	0	0
Short-term debt and current portion of long-term debt	0	0
Accounts payable and accrued liabilities	1,036	10
Intercompany payables	15	51
Other current liabilities	12	0
Total Current Liabilities	1,063	61
Long-term debt	792	107
Non-current deferred tax liabilities	0	0
Pension, other post-retirement and other post-employment liabilities	0	0
Intercompany payables	2,100	2,890
Other non-current liabilities	5	4
TOTAL LIABILITIES	3,960	3,062
TOTAL AON SHAREHOLDERS’ EQUITY	8,145	7,762
Noncontrolling interests	0	0
TOTAL EQUITY	8,145	7,762
TOTAL LIABILITIES AND EQUITY	12,105	10,824
Aon Corporation [Member]
CURRENT ASSETS :
Cash and cash equivalents	247	199	0	14
Short-term investments	163	89
Receivables, net	4	1
Fiduciary assets	0	0
Intercompany receivables	3,503	2,092
Other current assets	69	53
Total Current Assets	3,986	2,434
Goodwill	0	0
Intangible assets, net	0	0
Fixed assets, net	0	0
Investments	57	49
Non-current deferred tax assets	465	620
Intercompany receivables	2,178	1,997
Other non-current assets	95	115
Investment in subsidiary	11,694	10,208
TOTAL ASSETS	18,475	15,423
CURRENT LIABILITIES
Fiduciary liabilities	0	0
Short-term debt and current portion of long-term debt	0	429
Accounts payable and accrued liabilities	62	71
Intercompany payables	5,449	2,637
Other current liabilities	47	49
Total Current Liabilities	5,558	3,186
Long-term debt	2,512	2,515
Non-current deferred tax liabilities	0	0
Pension, other post-retirement and other post-employment liabilities	925	1,294
Intercompany payables	7,267	166
Other non-current liabilities	159	254
TOTAL LIABILITIES	16,421	7,415
TOTAL AON SHAREHOLDERS’ EQUITY	2,054	8,008
Noncontrolling interests	0	0
TOTAL EQUITY	2,054	8,008
TOTAL LIABILITIES AND EQUITY	18,475	15,423
Other Non-Guarantor Subsidiaries [Member]
CURRENT ASSETS :
Cash and cash equivalents	1,246	0	293	332
Short-term investments	360	257
Receivables, net	2,892	3,095
Fiduciary assets	11,871	12,214
Intercompany receivables	5,452	3,545
Other current assets	513	370
Total Current Assets	22,334	19,481
Goodwill	8,997	8,943
Intangible assets, net	2,578	2,975
Fixed assets, net	791	820
Investments	75	116
Non-current deferred tax assets	193	266
Intercompany receivables	2,201	2,350
Other non-current assets	1,228	908
Investment in subsidiary	0	0
TOTAL ASSETS	38,397	35,859
CURRENT LIABILITIES
Fiduciary liabilities	11,871	12,214
Short-term debt and current portion of long-term debt	707	23
Accounts payable and accrued liabilities	1,849	1,811
Intercompany payables	3,677	2,162
Other current liabilities	866	779
Total Current Liabilities	18,970	16,989
Long-term debt	378	1,091
Non-current deferred tax liabilities	1,025	1,024
Pension, other post-retirement and other post-employment liabilities	682	982
Intercompany payables	2,178	2,247
Other non-current liabilities	867	885
TOTAL LIABILITIES	24,100	23,218
TOTAL AON SHAREHOLDERS’ EQUITY	14,247	12,598
Noncontrolling interests	50	43
TOTAL EQUITY	14,297	12,641
TOTAL LIABILITIES AND EQUITY	38,397	35,859
Consolidating Adjustments [Member]
CURRENT ASSETS :
Cash and cash equivalents	(1,016)	(39)	(21)	0
Short-term investments	0	0
Receivables, net	0	0
Fiduciary assets	0	0
Intercompany receivables	(9,141)	(5,637)
Other current assets	(19)	0
Total Current Assets	(10,176)	(5,676)
Goodwill	0	0
Intangible assets, net	0	0
Fixed assets, net	0	0
Investments	0	0
Non-current deferred tax assets	(605)	(718)
Intercompany receivables	(11,545)	(4,513)
Other non-current assets	(99)	(107)
Investment in subsidiary	(16,301)	(20,606)
TOTAL ASSETS	(38,726)	(31,620)
CURRENT LIABILITIES
Fiduciary liabilities	0	0
Short-term debt and current portion of long-term debt	(4)	0
Accounts payable and accrued liabilities	(1,016)	(39)
Intercompany payables	(9,141)	(4,850)
Other current liabilities	(19)	3
Total Current Liabilities	(10,180)	(4,886)
Long-term debt	4	0
Non-current deferred tax liabilities	(605)	(718)
Pension, other post-retirement and other post-employment liabilities	0	0
Intercompany payables	(11,545)	(5,303)
Other non-current liabilities	(99)	(107)
TOTAL LIABILITIES	(22,425)	(11,014)
TOTAL AON SHAREHOLDERS’ EQUITY	(16,301)	(20,606)
Noncontrolling interests	0	0
TOTAL EQUITY	(16,301)	(20,606)
TOTAL LIABILITIES AND EQUITY	$ (38,726)	$ (31,620)