Goodwill and Other Intangible Assets - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Goodwill [Line Items]
Goodwill reclassified to assets held-for-sale	$ 1	$ 40
Amortization expense for other intangible assets	93	$ 121	$ 117
Concentra Inc.
Goodwill [Line Items]
Goodwill reclassified to assets held-for-sale	$ 480