Restructuring charges/other - Components of restructuring charges (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				18 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Mar. 31, 2015
Restructuring Cost And Reserve [Line Items]
Restructuring charges	$ (1)	[1]	$ 26
Gains on sales of assets	0		(37)
Other	(1)		0
Restructuring charges/other	(2)		(11)
2013 Actions
Restructuring Cost And Reserve [Line Items]
Severance and benefits cost	(1)	[1]	27	[1]
Other exit costs	0		5
Restructuring charges	(1)		32		74
Prior Actions
Restructuring Cost And Reserve [Line Items]
Severance and benefits cost	0	[1]	(6)	[1]
Other exit costs	0	[1]	(1)	[1]
Accelerated depreciation	0		1
Restructuring charges	$ 0		$ (6)

[1] Includes changes in estimates.