Shareholders' Equity - Reclassification Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014
Reclassification out of Accumulated Other Comprehensive Income
Investment income	$ 13	$ 24
Product sales revenue	2,682	2,905
Cost of product sales	(1,251)	(1,329)
Other interest expense	(41)	(40)
Income (loss) before provision for income taxes	386	373
Provision for income tax	(89)	(82)
Net income	297	291
Net gain on investments
Reclassification out of Accumulated Other Comprehensive Income
Provision for income tax	(7)	(38)	$ 5	$ (31)
Net gain on derivatives
Reclassification out of Accumulated Other Comprehensive Income
Provision for income tax	55	61	56	64
Net gains from pension and other postretirement plans
Reclassification out of Accumulated Other Comprehensive Income
Provision for income tax	71	70	$ 71	$ 70
Foreign Exchange Contract | Reclassification Out of Accumulated Other Comprehensive Income | Net gain on derivatives
Reclassification out of Accumulated Other Comprehensive Income
Product sales revenue	0	20
Cost of product sales	0	(3)
Income (loss) before provision for income taxes	(6)	11
Provision for income tax	2	0
Net income	(4)	11
Interest Rate Swap | Reclassification Out of Accumulated Other Comprehensive Income | Net gain on interest rate swap
Reclassification out of Accumulated Other Comprehensive Income
Other interest expense	(6)	(6)
Unrealized Gain on Investments | Reclassification Out of Accumulated Other Comprehensive Income | Net gain on investments
Reclassification out of Accumulated Other Comprehensive Income
Investment income	(2)	14
Provision for income tax	0	6
Net income	$ (2)	$ 8