Restructuring charges/other - Restructuring reserve (Details) (USD $)	12 Months Ended						15 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2014
Restructuring Reserve [Roll Forward]
Beginning accrual	$ 161,000,000		$ 349,000,000		$ 116,000,000
Restructuring charges	20,000,000	[1]	126,000,000	[1]	400,000,000	[1]
Non-cash items			(22,000,000)	[2]	(121,000,000)	[2]
Payments	(124,000,000)		(292,000,000)		(46,000,000)
Remaining accrual	57,000,000		161,000,000		349,000,000		57,000,000
2013 Actions
Restructuring Reserve [Roll Forward]
Restructuring charges	26,000,000		49,000,000		0		75,000,000
Prior Actions
Restructuring Reserve [Roll Forward]
Restructuring charges	(6,000,000)		77,000,000		400,000,000
Severance and benefits cost | 2013 Actions
Restructuring Reserve [Roll Forward]
Beginning accrual	49,000,000		0		0
Restructuring charges	16,000,000	[1]	49,000,000	[1]	0	[1]
Non-cash items			0	[2]	0	[2]
Payments	(43,000,000)		0		0		(43,000,000)
Remaining accrual	22,000,000		49,000,000		0		22,000,000
Severance and benefits cost | Prior Actions
Restructuring Reserve [Roll Forward]
Beginning accrual	105,000,000		340,000,000		109,000,000
Restructuring charges	(6,000,000)	[1]	36,000,000	[1]	251,000,000	[1]
Non-cash items			(5,000,000)	[2]	3,000,000	[2]
Payments	(73,000,000)		(266,000,000)		(23,000,000)
Remaining accrual	26,000,000		105,000,000		340,000,000		26,000,000
Other Charges | 2013 Actions
Restructuring Reserve [Roll Forward]
Beginning accrual	0		0		0
Restructuring charges	10,000,000	[1]	0	[1]	0	[1]
Non-cash items			0	[2]	0	[2]
Payments	(1,000,000)		0		0
Remaining accrual	9,000,000		0		0		9,000,000
Other Charges | Prior Actions
Restructuring Reserve [Roll Forward]
Beginning accrual	7,000,000		9,000,000		7,000,000
Restructuring charges	0	[1]	41,000,000	[1]	149,000,000	[1]
Non-cash items			(17,000,000)	[2]	(124,000,000)	[2]
Payments	(7,000,000)		(26,000,000)		(23,000,000)
Remaining accrual	$ 0		$ 7,000,000		$ 9,000,000		$ 0

[1] Includes changes in estimates.

[2] Reflects charges for goodwill impairment, stock-based compensation, impacts of postretirement benefit plans and accelerated depreciation.