Pension Plans and Other Postretirement Benefits - Benefit Obligations and Plan Assets (Details) - Pension Plan - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in benefit obligation:
Benefit obligation, beginning of year	$ 5,841	$ 131
Acquired benefit obligations	0	5,685
Interest cost	225	25	$ 20
Actuarial loss	530	41
Benefit payments	(357)	(41)
Benefit obligation, end of year	6,239	5,841	131
Change in plan assets:
Fair value of plan assets, beginning of year	5,663	0
Fair value of plan assets acquired	0	5,709
Actual return on plan assets	1,064	(17)
Employer contributions	25	12	46
Benefit payments	(357)	(41)
Fair value of plan assets, end of year	6,395	5,663	$ 0
Funded status	156	(178)
Assets (liabilities) recognized on the consolidated balance sheet
Non-current assets reflected in other assets	494	147
Current liabilities reflected in accrued expenses	(25)	(25)
Non-current liabilities reflected in other long-term liabilities	(313)	(300)
Net assets (liabilities)	$ 156	$ (178)

Amount of increase (decrease) in plan assets of defined benefit plan from actual return (loss) determined by change in fair value of plan assets adjusted for contributions, benefit payments, and other expenses.

Name:	us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of gain (loss) from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan.