Stock-Based Compensation Plans (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation costs	$ 143	$ 98	$ 105
Stock-based compensation costs capitalized	60	37	37
Incentive Plans \| Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation costs	102	49	62
Incentive Plans \| Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation costs	1	1	2
Incentive Plans \| Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation costs	0	0	(3)
401(k) Savings Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation costs	33	42	39
EDCP & DCPD
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation costs	$ 7	$ 6	$ 5

Represents the compensation cost capitalized during the period arising from equity-based compensation arrangements (for example, shares of stock, units, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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- Definition

Amount of capitalized and expensed compensation cost from equity-based compensation arrangements.

+ References

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