Commitments and Contingencies Level 4 - Unfunded Commitments (Details) $ in Millions	Dec. 31, 2017 USD ($)
Other Commitments [Abstract]
Other Commitment	$ 787
Commitments to Fund Limited Partnership and Other Alternative Investments	683
Commitment to fund Private placement securities	23
Commitments to Fund Mortgage Loans	$ 81

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