Consolidated Balance Sheets (Parenthetical) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Available-for-sale Debt Securities, Amortized Cost Basis	$ 20,914,000,000	$ 22,507,000,000
Available-for-sale Equity Securities, Amortized Cost Basis	$ 140,000,000	$ 142,000,000
Common Stock, Shares Authorized	1,000	1,000
Common Stock, Shares, Issued	1,000	1,000
Common Stock, Shares, Outstanding	1,000	1,000
Common Stock, Par or Stated Value Per Share	$ 5,690	$ 5,690
Commercial Loan [Member]
Allowance for Loan and Lease Losses, Real Estate	$ 0	$ 19,000,000