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Debt Narrative (Details) - USD ($) $ in Millions	3 Months Ended
Debt Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2018
Debt Instrument [Line Items]
Extinguishment of Debt, Amount	$ 1,128
Repayments of Debt	1,100
Gain on extinguishment of debt	18	$ 25
Write off of Deferred Debt Issuance Cost	$ 10
Junior subordinated debentures due February 2057, 5.875%
Debt Instrument [Line Items]
Debt Instrument, Interest Rate Terms	Our 5.875% Junior subordinated debentures due February 2057 and 6.250% Junior subordinated debentures due February 2057 accrue interest at the stated fixed rates until February 28, 2022 and February 28, 2027, respectively, on which dates the rates will switch to floating rates based on three-month LIBOR plus 3.895% and 3.899%, respectively, reset quarterly. These debentures can be called by us at any time after the expiration of the fixed-rate period.
Senior Notes and Senior and Junior Debentures
Debt Instrument [Line Items]
Unamortized net discount related to notes and debentures	$ 419		$ 431