Basis of Presentation and Significant Accounting Policies (Schedule of Operating Revenue, Net of Contractual Allowances and Discounts (But Before the Provision for Bad Debts)) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Health Care Organization, Receivable and Revenue Disclosures [Line Items]
Operating revenues (net of contractual allowances and discounts)	$ 5,754	$ 5,646
Medicare [Member]
Health Care Organization, Receivable and Revenue Disclosures [Line Items]
Operating revenues (net of contractual allowances and discounts)	1,431	1,398
Medicaid [Member]
Health Care Organization, Receivable and Revenue Disclosures [Line Items]
Operating revenues (net of contractual allowances and discounts)	593	586
Managed Care And Other Third Party Payors [Member]
Health Care Organization, Receivable and Revenue Disclosures [Line Items]
Operating revenues (net of contractual allowances and discounts)	3,022	2,946
Self-Pay [Member]
Health Care Organization, Receivable and Revenue Disclosures [Line Items]
Operating revenues (net of contractual allowances and discounts)	$ 708	$ 716