Accumulated Other Comprehensive (Loss) Income - Schedule of Changes in Components of AOCI (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, shareholders' equity	$ 9,662.0	$ 4,738.0
AOCI activity before reclassifications	53.0	(318.0)
Amounts reclassified from AOCI	13.0	3.0
Other comprehensive income for the period	66.0	(315.0)
Ending balance, shareholders' equity	19,216.0	10,570.0
Total AOCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, shareholders' equity	(735.0)	10.0
Other comprehensive income for the period	66.0	(315.0)
Ending balance, shareholders' equity	(669.0)	(305.0)
Unrealized (loss) gain on securities available for sale
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, shareholders' equity	(739.0)	(9.0)
AOCI activity before reclassifications	45.0	(318.0)
Amounts reclassified from AOCI	13.0	0.0
Other comprehensive income for the period	58.0	(318.0)
Ending balance, shareholders' equity	(681.0)	(327.0)
Unrealized loss on securities available for sale transferred to securities held to maturity
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, shareholders' equity	(6.0)	(7.0)
AOCI activity before reclassifications	0.0	0.0
Amounts reclassified from AOCI	0.0	1.0
Other comprehensive income for the period	0.0	1.0
Ending balance, shareholders' equity	(6.0)	(6.0)
Defined benefit pension items
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, shareholders' equity	10.0	26.0
AOCI activity before reclassifications	8.0	0.0
Amounts reclassified from AOCI	0.0	2.0
Other comprehensive income for the period	8.0	2.0
Ending balance, shareholders' equity	$ 18.0	$ 28.0