Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

No definition available.

Name:	us-gaap_SubsequentEventLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Subsequent Events - Additional Information (Detail) - USD ($) $ in Millions	Oct. 31, 2019	Dec. 31, 2017	Dec. 31, 2014
Subsequent Event [Line Items]
Commitment to purchase alternative investment		$ 50	$ 50
Subsequent Events
Subsequent Event [Line Items]
Commitment to purchase alternative investment	$ 10