Retirement Benefits (Unaudited) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Defined Contribution Plan [Abstract]
Defined contribution plan, employer contributions	$ 88	$ 88	$ 279	$ 192
Pension Benefits
Components of Net Periodic Benefit Cost
Service cost	92	100	184	199
Interest cost	340	300	680	590
Expected return on plan assets	(526)	(544)	(1,051)	(1,073)
Amortization of prior service credit	(14)	(14)	(29)	(29)
Net periodic benefit cost (benefit)	(108)	(158)	(216)	(313)
Defined benefit plan, contributions by Employer	23	23	46	45
OPB
Components of Net Periodic Benefit Cost
Service cost	4	5	8	10
Interest cost	20	19	40	38
Expected return on plan assets	(23)	(24)	(46)	(49)
Amortization of prior service credit	0	(6)	(1)	(11)
Net periodic benefit cost (benefit)	1	(6)	1	(12)
Defined benefit plan, contributions by Employer	$ 12	$ 11	$ 24	$ 22