Gypsum Transportation Limited (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				1 Months Ended	8 Months Ended
	Mar. 31, 2015 Ocean_vessel	Dec. 31, 2014	Mar. 31, 2014		Apr. 30, 2015 Agreement	Dec. 31, 2015
Long Lived Assets Held-for-sale [Line Items]
Net proceeds from asset dispositions	$ 1		$ 0
Long-term debt	2,206	2,209
Contract termination charge		6
Self-unloading ocean vessels	2
Affreightment term of contract	5 years
Operating profit (loss)	76		66	[1]
Ship mortgage facility
Long Lived Assets Held-for-sale [Line Items]
Long-term debt	18	21
Subsequent event
Long Lived Assets Held-for-sale [Line Items]
Memorandum of agreement for sale of ocean vessels					2
Net proceeds from asset dispositions					42
Costs associated with sale of property plant and equipment					1
Subsequent event | Minimum
Long Lived Assets Held-for-sale [Line Items]
Estimated expense of disposition of vessels and windup of GTL operations						8
Subsequent event | Maximum
Long Lived Assets Held-for-sale [Line Items]
Estimated expense of disposition of vessels and windup of GTL operations						11
Gypsum Transportation Limited
Long Lived Assets Held-for-sale [Line Items]
Operating profit (loss)	0		8
Self-unloading ocean vessels
Long Lived Assets Held-for-sale [Line Items]
Assets held for sale	$ 35

[1] Net sales and operating profit (loss) have been recast for the three months ended March 31, 2014 to conform with the new presentation of reportable segments.