Gypsum Transportation Limited (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Long Lived Assets Held-for-sale [Line Items]
Receivable per release and debt settlement agreement		$ 14
Loss on trade receivable from release and debt settlement agreement		9
Recovered receivable per release and debt settlement agreement	$ 8	$ 6
Recovery of receivable	0		$ 0	$ (3)	$ 0
Recovered receivable recorded in interest income				1
Recovered receivable recorded in other income				4
Operating profit	97		94	335	261
Gypsum Transportation Limited
Long Lived Assets Held-for-sale [Line Items]
Operating profit	$ 0		$ 0	$ 3	$ 1