Shareholders' Equity (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended		3 Months Ended	12 Months Ended
	Feb. 22, 2024	Feb. 23, 2023	Dec. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Schedule of Equity Method Investments [Line Items]
Preferred stock, authorized shares (in shares)			4,400,000	4,400,000	4,400,000
Liquidation preference of preferred stock (per share)				$ 1,000
Preferred stock, liquidation preference per depositary share (in dollars per share)				$ 25
Depositary share, preferred stock ownership interest				0.025%
Stock redemption						$ 126.0
Shares outstanding (in shares)				148,200,000
Common stock, par value (in dollars per share)			$ 0.001	$ 0.001	$ 0.001
Common stock and additional paid-in capital				$ 1,700.0
Common stock and additional paid-in capital decrease				$ 23.0
Common stock and additional paid-in capital decrease (as a percent)				1.00%
Common stock repurchased (in shares)		900,000			3,600,000
Fair value of stock repurchased		$ 50.0			$ 200.0
Average price per share of stock repurchased (in dollars per share)		$ 52.82			$ 56.13
Other comprehensive income (loss)				$ 420.0	$ (3,032.0)	(405.0)
Accumulated other comprehensive income (loss)			$ (3,112.0)	(2,692.0)	(3,112.0)
Transfer from available for sale to held-to-maturity, fair value			10,700.0	10,691.0
Investment securities available-for-sale transferred to held-to-maturity, at amortized cost (fair value $10,691)				0.0	13,097.0	0.0
Unrealized loss unamortized over the life of security				2,100.0
Unrealized loss unamortized over the life of security, after tax				1,500.0
Common stock held in trust			14.0	19.0	14.0
Total invested assets of trusts			114.0	124.0	114.0
Total obligations of trusts			$ 128.0	143.0	128.0
Fair value of stock repurchased				$ 51.0	$ 202.0	$ 800.0
Subsequent Event
Schedule of Equity Method Investments [Line Items]
Common stock repurchased (in shares)	900,000
Fair value of stock repurchased	$ 35.0
Average price per share of stock repurchased (in dollars per share)	$ 39.32