Advances (Prepayment Fees) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Advances [Abstract]
Prepayment Fees on Advances, Net	$ 9	$ 8	$ 2

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