Stock Based Incentive Compensation Plans (Summary of activity for stock options with performance conditions) (Details) - Stock options with performance conditions [Member] $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) $ / shares shares
Shares
Outstanding as of beginning of year (in shares) | shares	209,104
Granted - original (in shares) | shares	56,125
Exercised (includes shares tendered) (in shares) | shares	(17,687)
Forfeited or expired (in shares) | shares	(38,892)
Outstanding as of end of year (in shares) | shares	208,650
Vested or expected to vest as of end of year (in shares) | shares	190,370
Exercisable as of end of year (in shares) | shares	172,006
Summary of activity for stock options, additional disclosures [Abstract]
Weighted average exercise price as of beginning of year (in dollars per share) | $ / shares	$ 61.17
Weighted average exercise price granted - original (in dollars per share) | $ / shares	23.49
Weighted average exercise price exercised (includes shares tendered) (in dollars per share) | $ / shares	45.60
Weighted average exercise price forfeited or expired (in dollars per share) | $ / shares	59.29
Weighted average exercise price outstanding as of end of year (in dollars per share) | $ / shares	52.70
Weighted average exercise price vested or expected to vest as of end of year (in dollars per share) | $ / shares	54.74
Weighted average exercise price exercisable as of end of year (in dollars per share) | $ / shares	$ 57.21
Weighted average remaining contractual term outstanding as of end of year (in years)	2 years 2 months 12 days
Weighted average remaining contractual term vested or expected to vest as of end of year (in years)	2 years 10 days
Weighted average remaining contractual term exercisable as of end of year (in years)	1 year 9 months 25 days
Aggregate intrinsic value outstanding as of end of year | $	$ 2
Aggregate intrinsic value vested or expected to vest as of end of year | $	1
Aggregate intrinsic value exercisable as of end of year | $	$ 1