Basis of Presentation and Significant Accounting Policies (Narrative) (Details) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) state item	Dec. 31, 2017 USD ($) item	Dec. 31, 2016 USD ($) segment	Jan. 01, 2019 USD ($)	Jan. 01, 2018 USD ($)
Business Description [Abstract]
Number of hospitals owned and leased by the Company | item		113
Number of stand alone rehabilitation or psychiatric hospitals | item		2
Number of licensed beds | item		18,227
Number of States in which Entity Operates | state		20
Cost of Revenue, Policy [Abstract]
Corporate Office Costs		$ 181	$ 189	$ 197
Stock-based compensation expense		13	24	46
Marketable Securities, Policy [Abstract]
Change in Fair Value of Available for Sale Securities, Activity during the year, net of tax		(2)	8	(11)
Property and Equipment, Policy [Abstract]
Construction in Progress, Gross	$ 222	219	222
Interest Costs Capitalized		15	11	9
Purchases of property and equipment accrued in accounts payable		115	166
Non-cash investing activity through capital leases		6	31	179
Goodwill, Policy [Abstract]
Impairment of goodwill	1,419	0	1,419	1,395
Third-Party Reimbursement [Abstract]
Amounts due to third party payors	156	144	156
Amounts due from third party payors	153	155	153
Net Operating Revenues, Policy [Abstract]
Value of charity care services at the Company's standard charges included in contractual allowances		491	482	487
Estimated cost incurred by Company to provide charity care services		62	62	64
Patient accounts receivable, net of allowance for doubtful accounts	2,384	2,352	$ 2,384
Allowance for Doubtful Accounts, Policy [Abstract]
Number of Hospitals Sold | item			30
Electronic Health Records Reimbursement, Policy [Abstract]
Electronic health records incentive reimbursement under HITECH		4	$ 28	70
Electronic Health Records Incentive Reimbursement, Cash Received		4	41	123
Concentration of Credit Risk, Policy [Abstract]
Accounts receivable, net of contractual allowances	2,384	2,352	2,384
Accounting for the Impairment or Disposal of Long-Lived Assets
Goodwill allocated to hospital disposal group held for sale		186	357
Impairment and (gain) loss on sale of businesses, net		668	2,123	$ 1,919
Segment Reporting, Policy [Abstract]
Number of Operating Segments | segment				2
Adoption of ASC 606 [Member]
Net Operating Revenues, Policy [Abstract]
Provision for contractual allowance included in net operating revenues			197
Allowance for doubtful patient accounts	394		394
Patient accounts receivable, net of allowance for doubtful accounts	(591)		(591)
Concentration of Credit Risk, Policy [Abstract]
Accounts receivable, net of contractual allowances	(591)		(591)
ASU 2018-02 [Member]
New Accounting Pronouncements, Policy [Abstract]
Accumulated other comprehensive loss reclassified to accumulated deficit						$ 6
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Net Operating Revenues, Policy [Abstract]
Patient accounts receivable, net of allowance for doubtful accounts						3,900
Concentration of Credit Risk, Policy [Abstract]
Accounts receivable, net of contractual allowances						$ 3,900
Hospitals Sold or Deemed Held for Sale [Member]
Accounting for the Impairment or Disposal of Long-Lived Assets
Impairment of long-lived assets held for sale			388
Goodwill allocated to hospital disposal group held for sale			$ 7
Write-Off Promissory Note Received as Consideration For the Sale of Hospitals [Member]
Allowance for Doubtful Accounts, Policy [Abstract]
Number of Hospitals Sold | item			3
Accounting for the Impairment or Disposal of Long-Lived Assets
Impairment of long-lived assets held for sale		29
Adjustment for Carrying Value of Other Long-Lived Assets at Underperforming Hospitals [Member]
Accounting for the Impairment or Disposal of Long-Lived Assets
Impairment of long-lived assets held for sale	341	216
Medicare [Member]
Net Operating Revenues, Policy [Abstract]
Patient accounts receivable, net of allowance for doubtful accounts	220	283	$ 220
Concentration of Credit Risk, Policy [Abstract]
Accounts receivable, net of contractual allowances	220	$ 283	$ 220
Accounts receivable net of contractual allowances, percent		5.00%	4.00%
Electronic Health Records Incentive Reimbursements [Member]
Electronic Health Records Reimbursement, Policy [Abstract]
Deferred Revenue		$ 0
Minimum [Member] | ASU 2016-02 [Member] | Subsequent Event [Member]
New Accounting Pronouncements, Policy [Abstract]
Operating Lease, Right-of-Use Asset					$ 665
Operating Lease, Liability					665
Maximum [Member]
Physician Income Guarantees, Policy [Abstract]
Finite-Lived Intangible Assets, Net	10	$ 1	$ 10
Maximum [Member] | ASU 2016-02 [Member] | Subsequent Event [Member]
New Accounting Pronouncements, Policy [Abstract]
Operating Lease, Right-of-Use Asset					715
Operating Lease, Liability					$ 715
Capitalized Internal Use Software, Significant System Conversions [Member] | Minimum [Member]
Other Assets, Policy [Abstract]
Finite-Lived Intangible Assets, Weighted-Average Useful Life		8 years
Capitalized Internal Use Software, Significant System Conversions [Member] | Maximum [Member]
Other Assets, Policy [Abstract]
Finite-Lived Intangible Assets, Weighted-Average Useful Life		10 years
Capitalized Internal Use Software, Except Significant System Conversions [Member]
Other Assets, Policy [Abstract]
Finite-Lived Intangible Assets, Weighted-Average Useful Life		3 years
Finite-Lived Intangible Assets, Except Capitalized Internal-Use Software [Member]
Other Assets, Policy [Abstract]
Finite-Lived Intangible Assets, Weighted-Average Useful Life		2 years
Physician Recruitment Contracts [Member]
Physician Income Guarantees, Policy [Abstract]
Physicians recruitment agreement period		1 year
Term of Physician Recruitment Contract		3 years
Finite-Lived Intangible Assets, Net	$ 29	$ 24	$ 29
Land Improvements [Member] | Minimum [Member]
Property and Equipment, Policy [Abstract]
Property, Plant and Equipment, Useful Life		3 years
Land Improvements [Member] | Maximum [Member]
Property and Equipment, Policy [Abstract]
Property, Plant and Equipment, Useful Life		20 years
Building and Building Improvements [Member] | Minimum [Member]
Property and Equipment, Policy [Abstract]
Property, Plant and Equipment, Useful Life		5 years
Building and Building Improvements [Member] | Maximum [Member]
Property and Equipment, Policy [Abstract]
Property, Plant and Equipment, Useful Life		40 years
Furniture and Fixtures [Member] | Minimum [Member]
Property and Equipment, Policy [Abstract]
Property, Plant and Equipment, Useful Life		3 years
Furniture and Fixtures [Member] | Maximum [Member]
Property and Equipment, Policy [Abstract]
Property, Plant and Equipment, Useful Life		18 years
Certain Facility [Member]
Property and Equipment, Policy [Abstract]
Non-cash investing activity through capital leases		$ 6
Geographic Concentration Risk [Member] | Florida [Member] | Sales Revenue Net [Member]
Business Description [Abstract]
Concentration Risk, Percentage		14.30%	14.00%	13.60%
Geographic Concentration Risk [Member] | Texas [Member] | Sales Revenue Net [Member]
Business Description [Abstract]
Concentration Risk, Percentage		11.70%	10.90%	10.40%
Geographic Concentration Risk [Member] | Indiana [Member] | Sales Revenue Net [Member]
Business Description [Abstract]
Concentration Risk, Percentage		12.50%	11.60%	9.40%
Certain Hospitals [Member]
Accounting for the Impairment or Disposal of Long-Lived Assets
Impairment of long-lived assets held for sale		$ 668
Certain Hospitals [Member] | Hospitals Sold or Deemed Held for Sale [Member]
Accounting for the Impairment or Disposal of Long-Lived Assets
Impairment of long-lived assets held for sale		$ 423
Home Care [Member]
Segment Reporting, Policy [Abstract]
Percentage of Ownership Interest Sold				80.00%