Commitments and Contingencies - Schedule of Investment Commitments (Details) - Commitment to Invest $ in Millions	Sep. 30, 2018 USD ($)
Other Commitments [Line Items]
Unfunded investment commitment	$ 942
Other invested assets
Other Commitments [Line Items]
Unfunded investment commitment	859
Equity securities
Other Commitments [Line Items]
Unfunded investment commitment	31
Fixed maturity securities, available-for-sale
Other Commitments [Line Items]
Unfunded investment commitment	43
Other assets
Other Commitments [Line Items]
Unfunded investment commitment	$ 9

Minimum amount of other commitment not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in the taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions.

No definition available.

Name:	us-gaap_OtherCommitment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant