Subsequent Events (Details) $ / shares in Units, $ in Thousands, shares in Millions		2 Months Ended	12 Months Ended
	Feb. 17, 2022 $ / shares	Feb. 25, 2022 USD ($) shares	Dec. 31, 2021 USD ($) bank_branch $ / shares	Dec. 31, 2020 USD ($) $ / shares	Dec. 31, 2019 $ / shares
Subsequent Event [Line Items]
Cash dividend declared per common share (in dollars per share) | $ / shares			$ 0.78	$ 0.72	$ 0.68
Assets			$ 20,946,771	$ 17,794,374
Deposits			$ 18,241,179	$ 15,232,358
Reliant
Subsequent Event [Line Items]
Number of banking offices | bank_branch			25
Assets			$ 3,000,000
Total loans			2,380,000
Deposits			$ 2,500,000
Subsequent event | Common stock, par value $1 per share
Subsequent Event [Line Items]
Dividend date declared	Feb. 17, 2022
Cash dividend declared per common share (in dollars per share) | $ / shares	$ 0.21
Dividend payable date	Apr. 05, 2022
Dividend date of record	Mar. 15, 2022
Subsequent event | Series I perpetual non-cumulative preferred stock
Subsequent Event [Line Items]
Dividend date declared	Feb. 17, 2022
Preferred stock dividend per preferred share (in dollars per share) | $ / shares	$ 429.6875
Dividend payable date	Mar. 15, 2022
Dividend date of record	Feb. 28, 2022
Subsequent event | Depositary share on Series I perpetual non-cumulative preferred stock
Subsequent Event [Line Items]
Preferred stock dividend per preferred share (in dollars per share) | $ / shares	$ 0.4296875
Subsequent event | Reliant
Subsequent Event [Line Items]
Total fair value of consideration transferred		$ 597,000
Common stock issued		$ 596,000
Shares issued in acquisition (in shares) | shares		16.6
Converted stock options		$ 795
Cash		$ 624