Stock-Based Compensation Plans - Summary of Nonvested Restricted Stock Unit Activity (Details) - Restricted Stock Units (RSUs) [Member] - $ / shares		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning Balance	[1]	3,389,503
Granted		1,321,988
Vested		(1,845,300)
Forfeited		(65,046)
Undistributed vested awards	[2]	(507,804)
Ending Balance	[1]	2,293,341	3,389,503
Nonvested, Weighted Average Exercise Price (in usd per share)	[1]	$ 32.24
Granted, Weighted Average Grant Date Fair Value (in usd per share)		38.60	$ 34.98	$ 28.14
Vested, Weighted Average Exercise Price (in usd per share)		32.03
Forfeited, Weighted Average Exercise Price (in usd per share)		32.96
Undistributed Vested Awards, Weighted Average Grant Date Fair Value (in usd per share)	[2]	36.76
Nonvested, Weighted Average Exercise Price (in usd per share)	[1]	$ 35.06	$ 32.24
Fully Vested Stock Based Compensation Issued To Retirement Eligible Employees		1,131,487	1,488,383

[1] Excludes 1,131,487 and 1,488,383 of restricted stock units issued to retirement-eligible employees as of December 31, 2018 and 2017, respectively, as they are fully vested.

[2] Represents restricted stock units that vested but were not distributed to retirement-eligible employees during 2018.