Contractual interest rate for funds borrowed, under the debt agreement.

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 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Description of the interest rate as being fixed or variable, and, if variable, identification of the index or rate on which the interest rate is based and the number of points or percentage added to that index or rate to set the rate, and other pertinent information, such as frequency of rate resets.

+ References

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No definition available.

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- Definition

The net cash inflow or outflow in aggregate debt due to repayments and proceeds from additional borrowings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Financing Activities
-URI http://asc.fasb.org/extlink&oid=6513228

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- Definition

The cash outflow for a borrowing having initial term of repayment within one year or the normal operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3291-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Financing Activities
-URI http://asc.fasb.org/extlink&oid=6513228

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Debt Level 4 (Details) - USD ($) $ in Millions	9 Months Ended		119 Months Ended	600 Months Ended
Debt Level 4 (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016	Feb. 15, 2027	Feb. 12, 2067	Mar. 15, 2017
Debt Instruments [Line Items]
Repayment of debt	$ 416
Proceeds from the issuance of debt	$ 500	$ 0
Junior Subordinated Notes 3 month Libor plus Two Point One Two Five Percent Due Two Thousand Sixty Seven [Member]
Debt Instruments [Line Items]
Debt Instrument, Interest Rate Terms				three-month LIBOR plus 2.125%
Senior Note Five Point Three Seven Five Due in Two Thousand Seventeen [Member]
Debt Instruments [Line Items]
Debt Instrument, Interest Rate, Stated Percentage					5.375%
Scenario, Forecast [Member] \| Junior Subordinated Notes Four Point Three Nine Percent Due Two Thousand Twenty Seven [Member]
Debt Instruments [Line Items]
Debt Instrument, Interest Rate Terms			0.0439