Employee Benefit Plans - Narrative (Details) shares in Millions, $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019 USD ($)	Sep. 30, 2019 USD ($) shares
Compensation and Retirement Disclosure [Abstract]
Number of days used to compute performance period average closing price of restricted stock units		20 days
RSUs
Compensation and Retirement Disclosure [Abstract]
Awards granted (in shares) \| shares		1.1
Vesting period		3 years
Time-Vested RSUs
Compensation and Retirement Disclosure [Abstract]
Awards granted (in shares) \| shares		0.8
Performance-Based RSUs
Compensation and Retirement Disclosure [Abstract]
Awards granted (in shares) \| shares		0.3
Pension Benefits
Compensation and Retirement Disclosure [Abstract]
Employer contribution to tax-qualified defined benefit pension plans	$ 335	$ 635
Retiree Medical Benefits
Compensation and Retirement Disclosure [Abstract]
Discount rate	3.39%	3.39%
Decrease in projected benefit obligation due to plan amendment and remeasurement	$ 421
Offset to other comprehensive loss related to prior service credits	597
Actuarial loss	$ 176
Amortization period	7 years

Defined Benefit Plan, Projected Benefit Obligation, Amortization Period

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- Definition

The time period over which the stock closing prices are averaged to arrive at a per-share valuation for equity based awards such as Restricted Stock Units, Performance Share and other equity based awards.

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- Definition

Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan.

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- Definition

Amount of contribution received by defined benefit plan from employer which increases plan assets.

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- Definition

Amount of increase (decrease) in benefit obligation of defined benefit plan from change in terms of existing plan or initiation of new plan.

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Amount, before tax, of cost (credit) of benefit change attributable to participants' prior service from plan amendment or plan initiation of defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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Amount, before tax, of gain (loss) for (increase) decrease in value of benefit obligation for change in actuarial assumptions and increase (decrease) in value of plan assets from experience different from that assumed of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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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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