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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Retirement Benefits (Narrative) (Details) - USD ($) $ in Millions		3 Months Ended
	Dec. 31, 2019	Mar. 31, 2021	Mar. 31, 2020
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Contributions by employer		$ 29
Estimated future employer contributions in current fiscal year		100
United States
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost recognized		39	$ 37
United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost recognized		$ 39	$ 31
United Kingdom \| Non-U.S. Plans \| Geographic Concentration Risk
Defined Benefit Plan Disclosure [Line Items]
Concentration risk percentage	81.00%
Equity Funds \| United States
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage		64.00%
Actual asset allocation percentage of equity		65.00%
Equity Funds \| United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage		28.00%
Actual asset allocation percentage of equity		30.00%
Fixed Income Funds \| United States
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage		36.00%
Actual asset allocation percentage of equity		35.00%
Fixed Income Funds \| United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage		72.00%
Actual asset allocation percentage of equity		70.00%