Employee Stock Compensation Plans - Allocated Compensation, Assumptions and Shares Available (Details) - USD ($) shares in Millions, $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted Stock or Unit Expense	$ 94	$ 65	$ 73
Employee Stock Ownership Plan (ESOP), Compensation Expense	4	4	4
Stock or Unit Option Plan Expense	9	4	0
Total stock-based compensation (pre-tax)	107	73	77
Tax Benefit	(12)	(10)	(22)
Total stock-based compensation (net of tax)	$ 95	$ 63	$ 55
Stock Incentive Plan, 2006 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized (in shares)	20

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Amount, after tax, of expense for award under share-based payment arrangement.

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Amount of tax benefit for recognition of expense of award under share-based payment arrangement.

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The amount of plan compensation cost recognized during the period.

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Amount of noncash expense for award of restricted stock or unit under share-based payment arrangement.

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Number of shares authorized for issuance under share-based payment arrangement.

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Amount of noncash expense for option under share-based payment arrangement.

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