Shareholders' Equity - Comprehensive Capital Plan (Details) - USD ($)	3 Months Ended				12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Cash dividends declared per common share (in dollars per share)	$ 0.17	$ 0.17	$ 0.12	$ 0.105	$ 0.565	$ 0.38	$ 0.33
2018 Capital Plan [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Authorized amount of share repurchases	$ 1,225,000,000				$ 1,225,000,000
Common shares repurchased, value					820,000,000
2017 Capital Plan [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common shares repurchased, value					$ 325,000,000