Retirement Benefits (Unaudited) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Defined Contribution Plan [Abstract]
Defined contribution plan, employer contributions	$ 98	$ 104	$ 377	$ 296
Pension Benefits
Components of Net Periodic Benefit Cost
Service cost	92	102	276	301
Interest cost	340	316	1,020	906
Expected return on plan assets	(525)	(571)	(1,576)	(1,644)
Amortization of prior service credit	(15)	(15)	(44)	(44)
Net periodic benefit cost (benefit)	(108)	(168)	(324)	(481)
Defined benefit plan, contributions by Employer	18	273	64	318
OPB
Components of Net Periodic Benefit Cost
Service cost	4	5	12	15
Interest cost	20	20	60	58
Expected return on plan assets	(23)	(26)	(69)	(75)
Amortization of prior service credit	(1)	(5)	(2)	(16)
Net periodic benefit cost (benefit)	0	(6)	1	(18)
Defined benefit plan, contributions by Employer	$ 10	$ 10	$ 34	$ 32