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		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Health Care Organization, Receivable and Revenue Disclosures [Line Items]
Operating revenues (net of contractual allowances and discounts)	$ 4,333	$ 5,084	$ 14,323	$ 16,128
Medicare [Member]
Health Care Organization, Receivable and Revenue Disclosures [Line Items]
Operating revenues (net of contractual allowances and discounts)	961	1,170	3,268	3,866
Medicaid [Member]
Health Care Organization, Receivable and Revenue Disclosures [Line Items]
Operating revenues (net of contractual allowances and discounts)	478	531	1,538	1,676
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)	2,319	2,741	7,722	8,580
Self-Pay [Member]
Health Care Organization, Receivable and Revenue Disclosures [Line Items]
Operating revenues (net of contractual allowances and discounts)	$ 575	$ 642	$ 1,795	$ 2,006