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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-Topic 210
-SubTopic 10
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Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph e
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The cash outflow during the period from the repayment of aggregate short-term and long-term debt. Excludes payment of capital lease obligations.

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (b)
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Debt (Details) - Repayment - USD ($) $ in Millions					12 Months Ended
Debt (Details) - Repayment - USD ($) $ in Millions	May 15, 2018	Dec. 15, 2017	Jun. 02, 2017	Jun. 20, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument
Debt, principal amount repaid					$ 600	$ 657	$ 400
Senior Notes [Member] \| 5.80% Senior Notes due May 15, 2018 [Member]
Debt Instrument
Debt, principal amount repaid	$ 500
Interest rate (percent)	5.80%					5.80%
Senior Notes [Member] \| 5.75% Senior notes due December 15, 2017 [Member]
Debt Instrument
Debt, principal amount repaid		$ 450
Interest rate (percent)		5.75%
Senior Notes [Member] \| 6.25% Senior notes due June 20, 2016 [Member]
Debt Instrument
Debt, principal amount repaid				$ 400
Interest rate (percent)				6.25%
Junior Subordinated Debt [Member] \| 6.25% Fixed-to-floating rate junior subordinated debentures due March 15, 2067 [Member]
Debt Instrument
Debt, principal amount repaid			$ 107
Interest rate (percent)			6.25%
Percentage of principal amount at which redemption price was set			100.00%