Segment Information - Schedule of fiduciary investment income by business segment (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Fiduciary investment income	$ 7	$ 7	$ 6	$ 6	$ 7	$ 8	$ 6	$ 7	$ 26	$ 28	$ 38
Risk Solutions [Member]
Segment Reporting Information [Line Items]
Fiduciary investment income									26	28	38
HR Solutions [Member]
Segment Reporting Information [Line Items]
Fiduciary investment income									$ 0	$ 0	$ 0