Insurance and Contractholder Liabilities - Liability Details for Unpaid Claims and Claim Expenses (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Group Disability and Other and International Markets
Liability for Claims and Claims Adjustment Expense [Line Items]
Unpaid claims and claim expenses	$ 6,235
Unpaid claims and claim expenses		$ 5,857
Group Disability and Other
Liability for Claims and Claims Adjustment Expense [Line Items]
Unpaid claims and claim expenses	5,368
Unpaid claims and claim expenses		5,076
Group Disability and Life
Liability for Claims and Claims Adjustment Expense [Line Items]
Unpaid claims and claim expenses	5,206
Unpaid claims and claim expenses		4,887
Other Operations
Liability for Claims and Claims Adjustment Expense [Line Items]
Unpaid claims and claim expenses	162
Unpaid claims and claim expenses		189
International Markets
Liability for Claims and Claims Adjustment Expense [Line Items]
Unpaid claims and claim expenses	$ 867
Unpaid claims and claim expenses		$ 781