Acquisitions - Additional Information (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
	Jun. 01, 2015	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale of business		$ 267	$ 0	$ 267	$ 0
Liabilities
Net assets disposed	$ 763					$ 737
Concentra Inc.
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Selling price in cash	1,055
Disposal transaction costs	25
Gain on sale of business		267		267
Revenues		166		411
Pretax earnings		$ 8		$ 15
Assets
Receivables, net	130					115
Property and equipment, net	197					191
Goodwill	480					480
Other intangible assets, net	124					131
Other assets	27					26
Total assets disposed/held-for-sale	958					943
Liabilities
Trade accounts payable and accrued expenses	81					90
Other liabilities	114					116
Total liabilities disposed/held-for-sale	$ 195					$ 206