Mergers, Acquisitions and Dispositions - Integration and Transaction-Related Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Before-tax
Interest expense on newly-issued debt	$ 0	$ 0	$ 227
Net investment income on debt proceeds	0	0	(123)
Charitable contributions	0	0	200
Legal and advisory fees	48	53	204
Bridge facility fees	0	0	140
All other integration and transaction-related costs	479	499	204
Integration and transaction-related costs, net	527	552	852
After-tax
Interest expense on newly-issued debt	0	0	179
Net investment income on debt proceeds	0	0	(97)
Charitable contributions	0	0	158
Legal and advisory fees	36	41	185
Bridge facility fees	0	0	111
All other integration and transaction-related costs	368	386	133
Integration and transaction-related costs, net	$ 404	$ 427	$ 669