Liabilities for Unpaid Claims and Claims Expenses - Liability Balance Details (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Group Disability and Life, Global Supplemental Beneftits and Other Operations [Member]
Liability For Unpaid Claims And Claims Adjustment Expense [Line Items]
Total liability for unpaid claims and claims expenses	$ 5,077	$ 4,889
Group Disability And Life Segment [Member]
Liability For Unpaid Claims And Claims Adjustment Expense [Line Items]
Total liability for unpaid claims and claims expenses	4,442	4,288
Global Supplemental Benefits Segment [Member]
Liability For Unpaid Claims And Claims Adjustment Expense [Line Items]
Total liability for unpaid claims and claims expenses	453	392
Other Operations Segment [Member]
Liability For Unpaid Claims And Claims Adjustment Expense [Line Items]
Total liability for unpaid claims and claims expenses	$ 182	$ 209