Restructuring Costs (Restructuring Activities) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Restructuring Reserve [Roll Forward]
Liability at beginning of period	$ 124	$ 170
Amounts Accrued	2	22
Cash Paid	(15)	(65)
Other		(3)
Liability at end of period	111	124
Severance [Member]
Restructuring Reserve [Roll Forward]
Liability at beginning of period	11	36
Amounts Accrued	0	9
Cash Paid	(3)	(33)
Other		(1)
Liability at end of period	8	11
Future Rent Under Non-Cancelable Leases and Other Costs [Member]
Restructuring Reserve [Roll Forward]
Liability at beginning of period	113	134
Amounts Accrued	2	13
Cash Paid	(12)	(32)
Other		(2)
Liability at end of period	103	113
Corporate Segment [Member]
Restructuring Reserve [Roll Forward]
Amounts Accrued	$ 2