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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Stock-Based Compensation - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total compensation expense for stock-based compensation plans	$ 96,000,000	$ 99,000,000	$ 104,000,000
Total income tax benefit recognized for stock-based compensation plans	$ 23,000,000	$ 23,000,000	$ 39,000,000
Common Shares available for future grant under compensation plans (in shares)	59,991,178
Maximum percentage of outstanding common stock that may be granted as options	6.00%
Rolling period in which a certain percentage of common stock cannot be granted as options	3 years
Exercise rate of stock options granted to employees	25.00%
Vesting period for compensation cost	4 years
Authorized number of shares that may be issued as equity awards (in shares)	71,600,000
Common shares, shares issued (in shares)	1,256,702,081	1,256,702,081
Weighted-average grant-date fair value of options (in dollars per share)	$ 3.07	$ 5.12	$ 4.60
Number of options, exercised (in shares)	2,039,208
Total intrinsic value of exercised options	$ 18,000,000	$ 21,000,000	$ 31,000,000
Cash received from options exercised	18,000,000	20,000,000	25,000,000
Actual tax benefit realized for tax deductions from options exercised	$ 1,000,000	$ 1,000,000	$ 4,000,000
Mandatory deferred incentive awards, vesting rate (as a percent)	25.00%
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares, shares issued (in shares)	3,000,000
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options expiration years	10 years
Number of options, exercised (in shares)	2,039,208	1,960,444	3,755,177
Unrecognized compensation cost related to nonvested options expected to vest	$ 2,000,000
Weighted-average period	2 years
Stock Options [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period for compensation cost	1 year
Stock Options [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options expiration years	10 years
Deferred Cash Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage	25.00%
Restricted Stock Unit [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage	25.00%
Equity Based Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Cash Performance Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Deferred Compensation Plans and Other Restricted Stock Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant-date fair value granted (in dollars per share)	$ 17.57	$ 20.77	$ 18.55
Deferred Compensation Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to nonvested options expected to vest	$ 17,000,000
Weighted-average period	4 years
Fair value of units/shares vested	$ 19,000,000	$ 22,000,000	$ 21,000,000
Long-Term Incentive Compensation Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to nonvested options expected to vest	$ 87,000,000
Weighted-average period	2 years 3 months 18 days
Fair value of units/shares vested	$ 89,000,000	$ 93,000,000	$ 76,000,000
Weighted-average grant-date fair value granted (in dollars per share)	$ 18.25	$ 19.28	$ 19.82
Discounted Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee discount on the purchase of stock through Discounted Stock Purchase Plan	10.00%
Purchases are limited to any month	$ 10,000
Purchases are limited to any calendar year	$ 50,000
Issuance of common shares (in shares)	327,243	327,435	257,738
Weighted-average cost of common shares issued under the plan (in dollars per share)	15.73	17.48	16.61
Vesting Contingent On Performance And Service Conditions, Payable In Stock [Member] \| Long-Term Incentive Compensation Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of performance units vested (in shares)	855,233
Weighted-average grant-date fair value granted (in dollars per share)	$ 17.51
Vesting Contingent On Performance And Service Conditions, Payable In Stock [Member] \| Long-Term Incentive Compensation Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of performance units vested (in shares)		508,799
Vesting Contingent On Performance And Service Conditions, Payable In Stock [Member] \| Long-Term Incentive Compensation Program [Member] \| Performance Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of units/shares vested	$ 9,000,000	$ 7,000,000
Vesting Contingent On Performance And Service Conditions, Payable In Cash [Member] \| Long-Term Incentive Compensation Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of performance units vested (in shares)	1,139,582
Weighted-average grant-date fair value granted (in dollars per share)	$ 20.33
Vesting Contingent On Performance And Service Conditions, Payable In Cash [Member] \| Long-Term Incentive Compensation Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of performance units vested (in shares)		561,313
Vesting Contingent On Performance And Service Conditions, Payable In Cash [Member] \| Long-Term Incentive Compensation Program [Member] \| Performance Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of units/shares vested	$ 20,000,000	$ 12,000,000