Gypsum Transportation Limited (Details) $ in Millions	1 Months Ended	3 Months Ended			6 Months Ended
	Apr. 30, 2015 USD ($)	Jun. 30, 2015 USD ($) Ocean_vessel	Mar. 31, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) Ocean_vessel	Jun. 30, 2014 USD ($)
Long Lived Assets Held-for-sale [Line Items]
Self-unloading ocean vessels | Ocean_vessel		2			2
Net proceeds from asset dispositions	$ 42				$ 42	$ 14
Gain on asset dispositions					7	12
Costs paid for contract termination	7
Business exit costs		$ 6
Gain on disposal of shipping operations, net		1		$ 0	1	0
Restricted cash and cash equivalents		2			2
Operating profit		105		98	181	164	[1]
Ship mortgage facility
Long Lived Assets Held-for-sale [Line Items]
Repayment of debt		18	$ 1
Gypsum Transportation Limited
Long Lived Assets Held-for-sale [Line Items]
Operating profit		$ 1		$ 6	$ 1	$ 14
Self-unloading ocean vessels [Member]
Long Lived Assets Held-for-sale [Line Items]
Gain on asset dispositions	$ 7

[1] Net sales and operating profit (loss) have been recast for the periods prior to April 1, 2014 to conform with the new presentation of reportable segments.