Restructuring (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended		3 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended
	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2013 Aon Hewitt Restructuring Plan [Member]	Jun. 30, 2013 Aon Hewitt Restructuring Plan [Member]	Jun. 30, 2013 Aon Hewitt Restructuring Plan [Member] HR Solutions [Member]	Jun. 30, 2013 Aon Hewitt Restructuring Plan [Member] HR Solutions [Member]	Jun. 30, 2013 Aon Hewitt Restructuring Plan [Member] Risk Solutions [Member]	Jun. 30, 2013 Aon Hewitt Restructuring Plan [Member] Risk Solutions [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges			$ 53	$ 79	$ 36	$ 51	$ 17	$ 28
Restructuring reserve	108	166
Cash payments	$ 58