Share-Based Compensation (Summary Of Changes In Nonvested Stock Units) (Details)	3 Months Ended
	Mar. 31, 2020 $ / shares shares
Restricted Stock Units (RSUs)
Shares [Roll Forward]
Nonvested at beginning of period (in shares) | shares	4,525,900
Granted (in shares) | shares	3,836,000.0
Vested (in shares) | shares	(1,909,100)
Cancelled/forfeited (in shares) | shares	(330,900)
Nonvested at period end (in shares) | shares	6,121,900
Weighted-Average Grant Date Fair Value [Roll Forward]
Granted, weighted-average grant date fair value, beginning of period (in dollars per share) | $ / shares	$ 27.44
Granted, weighted-average grant date fair value (in dollars per share) | $ / shares	9.27
Vested, weighted average grant date fair value (in dollars per share) | $ / shares	27.16
Cancelled/forfeited, weighted-average grant date fair value (in dollars per share) | $ / shares	15.71
Granted, weighted-average grant date fair value, period end ( in dollars per share) | $ / shares	$ 18.43
Performance Share Units
Shares [Roll Forward]
Nonvested at beginning of period (in shares) | shares	3,817,700
Granted (in shares) | shares	2,828,400
Vested (in shares) | shares	(1,364,400)
Cancelled/forfeited (in shares) | shares	(441,000.0)
Nonvested at period end (in shares) | shares	4,840,700
Weighted-Average Grant Date Fair Value [Roll Forward]
Granted, weighted-average grant date fair value, beginning of period (in dollars per share) | $ / shares	$ 28.52
Granted, weighted-average grant date fair value (in dollars per share) | $ / shares	10.02
Vested, weighted average grant date fair value (in dollars per share) | $ / shares	31.65
Cancelled/forfeited, weighted-average grant date fair value (in dollars per share) | $ / shares	20.62
Granted, weighted-average grant date fair value, period end ( in dollars per share) | $ / shares	$ 17.55