Insurance and Contractholder Liabilities - Liability Details for Unpaid Claims and Claim Expenses (Details) - USD ($) $ in Millions	Mar. 31, 2020	Mar. 31, 2019
Group Disability and Other and International Markets
Liability for Claims and Claims Adjustment Expense [Line Items]
Unpaid claims and claim expenses	$ 6,119
Unpaid claims and claim expenses		$ 5,725
Group Disability and Other
Liability for Claims and Claims Adjustment Expense [Line Items]
Unpaid claims and claim expenses	5,293
Unpaid claims and claim expenses		4,980
Group Disability and Life
Liability for Claims and Claims Adjustment Expense [Line Items]
Unpaid claims and claim expenses	5,084
Unpaid claims and claim expenses		4,786
Other Operations
Liability for Claims and Claims Adjustment Expense [Line Items]
Unpaid claims and claim expenses	209
Unpaid claims and claim expenses		194
International Markets
Liability for Claims and Claims Adjustment Expense [Line Items]
Unpaid claims and claim expenses	$ 826
Unpaid claims and claim expenses		$ 745