Accumulated Other Comprehensive Income (Loss) - Schedule of Changes in Components of AOCI (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, shareholders' equity	$ 10,570.0	$ 4,321.0	$ 4,738.0	$ 4,229.0
AOCI activity before reclassifications			(481.0)	(25.0)
Amounts reclassified from AOCI			6.0	(9.0)
Net current period AOCI	(160.0)	12.0	(475.0)	(34.0)
Ending balance, shareholders' equity	10,642.0	4,477.0	10,642.0	4,477.0
Total AOCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, shareholders' equity	(305.0)	(34.0)	10.0	12.0
Net current period AOCI	(160.0)	12.0	(475.0)	(34.0)
Ending balance, shareholders' equity	(465.0)	(22.0)	(465.0)	(22.0)
Unrealized (loss) gain on securities available for sale
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, shareholders' equity			(9.0)	79.0
AOCI activity before reclassifications			(481.0)	(25.0)
Amounts reclassified from AOCI			0.0	(19.0)
Net current period AOCI			(481.0)	(44.0)
Ending balance, shareholders' equity	(490.0)	35.0	(490.0)	35.0
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			(7.0)	4.0
AOCI activity before reclassifications			0.0	0.0
Amounts reclassified from AOCI			1.0	0.0
Net current period AOCI			1.0	0.0
Ending balance, shareholders' equity	(6.0)	4.0	(6.0)	4.0
Defined benefit pension items
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, shareholders' equity			26.0	(71.0)
AOCI activity before reclassifications	0.0	0.0	0.0	0.0
Amounts reclassified from AOCI			5.0	10.0
Net current period AOCI	3.0	5.0	5.0	10.0
Ending balance, shareholders' equity	$ 31.0	$ (61.0)	$ 31.0	$ (61.0)