Stock-Based Compensation Plans - Summary of Nonvested Restricted Stock Unit Activity (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Share-based Payment Arrangement, Nonvested Award, Excluding Option, Cost Not yet Recognized, Amount	$ 17
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning Balance	2,293,341
Granted	902,857
Vested	(1,232,704)
Forfeited	(33,603)
Undistributed vested awards	(431,178)
Ending Balance	1,498,713	2,293,341
Nonvested, Weighted Average Exercise Price (in usd per share)	$ 40.35	$ 35.06
Granted, Weighted Average Grant Date Fair Value (in usd per share)	45.65	$ 38.60	$ 34.98
Vested, Weighted Average Exercise Price (in usd per share)	32.83
Forfeited, Weighted Average Exercise Price (in usd per share)	39.01
Undistributed Vested Awards, Weighted Average Grant Date Fair Value (in usd per share)	$ 44.75
Fully Vested Stock Based Compensation Issued To Retirement Eligible Employees	863,196	1,131,487
Fair Value Of Settled Restricted Stock Units	$ 92	$ 106	$ 88
Share-based Payment Arrangement, Nonvested Award, Excluding Option, Cost Not yet Recognized, Amount	$ 28
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition	2 years 9 months 18 days
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning Balance	3,403,228
Granted	1,089,903
Vested	(1,610,146)
Forfeited	(25,249)
Undistributed vested awards	(348,363)
Ending Balance	1,709,755	3,403,228
Nonvested, Weighted Average Exercise Price (in usd per share)	$ 39.21	$ 33.13
Granted, Weighted Average Grant Date Fair Value (in usd per share)	47.37	$ 38.15	$ 35.00
Vested, Weighted Average Exercise Price (in usd per share)	28.90
Forfeited, Weighted Average Exercise Price (in usd per share)	45.03
Undistributed Vested Awards, Weighted Average Grant Date Fair Value (in usd per share)	$ 48.82
Fully Vested Stock Based Compensation Issued To Retirement Eligible Employees	2,017,870	3,586,259
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition	1 year 7 months 6 days

Fair value of settled restricted stock

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Fully vested stock based compensation issued to retirement-eligible employees

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Represents restricted stock units that are vested but not distributed to retirement-eligible employees.

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No definition available.

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- Definition

Represents the weighted average exercise price of equity instruments other than options that vested but were not distributed to retirement eligible employees.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Amount of cost to be recognized for nonvested award under share-based payment arrangement. Excludes share and unit options.

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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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- Definition

Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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- Definition

The number of grants made 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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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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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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