Derivative Instruments and Hedging Activities (Basis Adjustments for Hedged Items) (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Derivative Instruments, Gain (Loss) [Line Items]
Cumulative amount of fair value hedging adjustment included in the carrying amount of the hedged item	$ 61.0
Total debt securities	11,040.0	$ 11,759.0
Amount of hedging	3,500.0
Fair Value Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Par value of hedged assets	11,885.0	12,389.0
Carrying amount of hedged assets	11,587.0	12,209.0
Cumulative amount of fair value hedging adjustment included in the carrying amount of the hedged item	(299.0)	$ (180.0)
Total debt securities	$ 10,800.0