Gypsum Transportation Limited (Details) $ in Millions	1 Months Ended	3 Months Ended								12 Months Ended
	Apr. 30, 2015 USD ($) ocean_vessel	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Property, Plant and Equipment [Line Items]
Self-unloading ocean vessels | ocean_vessel	2
Long-lived asset impairment charges							$ 30			$ 0	$ 90	$ 0
Contract termination charge											6
Provision for bad debt										0	1	0
Proceeds from sale of assets										61	16	2
Gain on asset disposition										15	12	1
Early termination costs paid	$ 7
Cost to exit shipping operations				$ 6
Gain on disposal of shipping operations, net										1	0	0
Contract termination and (recovery) loss on receivable						$ 15				(6)	15	0
Operating profit (loss)		$ 98	$ 102	$ 105	$ 76	(24)	$ 22	$ 98	$ 66	381	162	258
Gypsum Transportation Limited
Property, Plant and Equipment [Line Items]
Operating profit (loss)										7	(52)	$ 20
GTL trading partner
Property, Plant and Equipment [Line Items]
Provision for bad debt											9
Receivable per release and debt settlement agreement		14								14
Loss on trade receivable		9								9
Remaining receivable that will be recorded when realization is assured		$ 5								$ 5
Self-unloading ocean vessels
Property, Plant and Equipment [Line Items]
Long-lived asset impairment charges						$ 60					$ 60
Proceeds from sale of assets	42
Gain on asset disposition	$ 7