Advances (Prepayment Fees) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Advances [Abstract]
Prepayment fees on advances, net	$ 3	$ 0

Amount of income earned, after hedging basis adjustments, from fees charged for prepayment of certain Federal Home Loan Bank (FHLBank) advances before original maturity.

No definition available.

Name:	us-gaap_PrepaymentFeesOnAdvancesNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration