For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

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Percentage of fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of plan assets held.

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Amount of cost for defined contribution plan.

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Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

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Maximum percentage of employee gross pay the employee may contribute to a defined contribution plan.

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Retirement Benefits (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended	9 Months Ended
	Oct. 31, 2016	Sep. 30, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Employer matching contribution, percent of employees' gross pay (up to)	4.00%
Maximum annual contributions per employee, percent	7.00%
Contributions by employer		$ 193
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Estimated future employer contributions in current fiscal year		63
United States
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost recognized		$ 99
United States \| Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage		64.00%
Actual asset allocation percentage of equity		65.00%
United States \| Fixed Income Funds
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage		36.00%
Actual asset allocation percentage of equity		35.00%
United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost recognized		$ 56
United Kingdom \| Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage			46.00%
Actual asset allocation percentage of equity		47.00%
United Kingdom \| Fixed Income Funds
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage			54.00%
Actual asset allocation percentage of equity		53.00%
United Kingdom \| Geographic Concentration Risk \| Non-U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Concentration risk percentage		81.00%