Restructuring Costs (Restructuring Activities) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Restructuring Reserve [Roll Forward]
Liability at beginning of period	$ 92	$ 124
Amounts Accrued	8	12
Cash Paid	(24)	(43)
Other	(2)	(1)
Liability at end of period	74	92
Severance [Member]
Restructuring Reserve [Roll Forward]
Liability at beginning of period	7	11
Amounts Accrued	3	4
Cash Paid	(5)	(8)
Other	(1)	0
Liability at end of period	4	7
Future Rent Under Non-Cancelable Leases and Other Costs [Member]
Restructuring Reserve [Roll Forward]
Liability at beginning of period	85	113
Amounts Accrued	5	8
Cash Paid	(19)	(35)
Other	(1)	(1)
Liability at end of period	70	$ 85
Risk and Insurance Services Segment [Member]
Restructuring Reserve [Roll Forward]
Amounts Accrued	3
Corporate Segment [Member]
Restructuring Reserve [Roll Forward]
Amounts Accrued	$ 5