Liabilities for Unpaid Claims and Claims Expenses - Reconciliation to the Liability for Unpaid Claims and Claims Expense (Details) - USD ($) $ in Millions	Jun. 30, 2018	Jun. 30, 2017
Group Disability and Life, Global Supplemental Beneftits and Other Operations [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total liability for unpaid claims and claims expenses	$ 5,246	$ 5,039
Group Disability And Life Segment [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total liability for unpaid claims and claims expenses	4,573	4,400
Global Supplemental Benefits Segment [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total liability for unpaid claims and claims expenses	480	452
Other Operations Segment [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total liability for unpaid claims and claims expenses	$ 193	$ 187