Accounting Policies - Related Party Transactions (Details) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018 USD ($) state	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) state	Sep. 30, 2017 USD ($)
Related Party Transaction
Expenses from transactions with related party	$ 4	$ 5	$ 34	$ 29
Equity Method Investee
Related Party Transaction
Other revenues from transactions with related party	$ 34	$ 36	$ 105	$ 106
Heartland Healthcare Services
Related Party Transaction
Number of states in which entity operates \| state	4		4

The number of states the entity operates in as of the balance sheet date.

No definition available.

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Period Type:	instant

- Definition

Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

Reflects the sum of all other revenue and income realized from sales and other transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party during the period.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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- Details

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- Details

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