Retirement Benefits - Fair Values of Pension Benefit Assets (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Defined Benefit Plan, Plan Assets, Category [Line Items]
Fair value of plan assets	$ 1,816	$ 1,764
Cash and cash equivalents
Defined Benefit Plan, Plan Assets, Category [Line Items]
Fair value of plan assets	32	36
Fixed maturity securities
Defined Benefit Plan, Plan Assets, Category [Line Items]
Fair value of plan assets	704	620
Equity securities
Defined Benefit Plan, Plan Assets, Category [Line Items]
Fair value of plan assets	269	378
Mutual funds
Defined Benefit Plan, Plan Assets, Category [Line Items]
Fair value of plan assets	48	44
Insurance company contracts
Defined Benefit Plan, Plan Assets, Category [Line Items]
Fair value of plan assets	142	143
Collective investment trusts
Defined Benefit Plan, Plan Assets, Category [Line Items]
Fair value of plan assets	484	413
Commingled fund
Defined Benefit Plan, Plan Assets, Category [Line Items]
Fair value of plan assets	86	69
Partnerships
Defined Benefit Plan, Plan Assets, Category [Line Items]
Fair value of plan assets	$ 51	$ 61