Fair Value (Financal assets and liabilities not measure at fair value) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Financial Assets [Abstract]
Mortgage loans	$ 864	$ 839
Financial Liabilities [Abstract]
Short term debt	30	150
Long term debt	2,679	2,708
Carrying Amount
Financial Assets [Abstract]
Mortgage loans	864	839
Note receivable	34	46
Financial Liabilities [Abstract]
Short term debt	30	150
Long term debt	2,679	2,708
Estimated Fair Value
Financial Assets [Abstract]
Mortgage loans	856	844
Note receivable	34	46
Financial Liabilities [Abstract]
Short term debt	30	150
Long term debt	2,786	2,896
Level 1 \| Estimated Fair Value
Financial Assets [Abstract]
Mortgage loans	0	0
Note receivable	0	0
Financial Liabilities [Abstract]
Short term debt	0	0
Long term debt	0	0
Level 2 \| Estimated Fair Value
Financial Assets [Abstract]
Mortgage loans	0	0
Note receivable	0	0
Financial Liabilities [Abstract]
Short term debt	30	150
Long term debt	2,786	2,896
Level 3 \| Estimated Fair Value
Financial Assets [Abstract]
Mortgage loans	856	844
Note receivable	34	46
Financial Liabilities [Abstract]
Short term debt	0	0
Long term debt	$ 0	$ 0

For an unclassified balance sheet, the amount due from customers or clients for goods or services that have been delivered or sold in the normal course of business, reduced to their estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(3))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(4))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(9))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(5))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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- Definition

The balance represents the amount of loans that are secured by real estate mortgages, offset by the reserve to cover probable credit losses on the loan portfolio.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1(c))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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