We have defined benefit pension plans, some of which are subject to collective bargaining agreements, that cover most of our employees. These plans provide eligible employees with retirement income based primarily on years of service and compensation during specific periods under final average pay and cash balance formulas. We fund all of our pension plans as required by local regulations. In the U.S., all qualified pension plans are subject to the Employee Retirement Income Security Act’s minimum funding standard. We typically do not fund or fully fund U.S. nonqualified and certain international pension plans that are not subject to funding requirements because contributions to these pension plans may be less economic and investment returns may be less attractive than our other investment alternatives.

We also provide health care and life insurance benefits for certain retired employees through our postretirement benefit plans. Most of our employees become eligible for these benefits if, while still working for us, they reach normal retirement age or take early retirement. These plans are unfunded, and retired employees share the cost with us. Individuals who became our employees as a result of an acquisition became eligible for postretirement benefits under our plans as determined by the terms of the relevant acquisition agreement.

The changes in benefit obligation related to all of our defined benefit plans, the changes in fair value of plan assets(a), and the funded status of our defined benefit plans as of and for the years ended below were as follows (in millions):


	Pension Plans				Other Postretirement Benefit Plans
	December 31,				December 31,
	2020		2019		2020		2019
Changes in benefit obligation
Benefit obligation as of beginning of year	$	3,239	$	2,639	$	336	$	292
Service cost	140		119		6		5
Interest cost	85		98		9		11

Participant contributions	—		—		12		11




Benefits paid	(195)		(154)		(28)		(29)
Actuarial loss	339		528		23		41
Other	17		9		—		5

Benefit obligation as of end of year	$	3,625	$	3,239	$	358	$	336

Changes in plan assets (a)
Fair value of plan assets as of beginning of year	$	2,709	$	2,236	$	—	$	—
Actual return on plan assets	413		490		—		—
Valero contributions	129		128		16		18
Participant contributions	—		—		12		11

Benefits paid	(195)		(154)		(28)		(29)
Other	11		9		—		—

Fair value of plan assets as of end of year	$	3,067	$	2,709	$	—	$	—

Reconciliation of funded status (a)
Fair value of plan assets as of end of year	$	3,067	$	2,709	$	—	$	—
Less: Benefit obligation as of end of year	3,625		3,239		358		336
Funded status as of end of year	$	(558)	$	(530)	$	(358)	$	(336)

Accumulated benefit obligation	$	3,398	$	3,039	n/a		n/a

(a)Plan assets include only the assets associated with pension plans subject to legal minimum funding standards. Plan assets associated with U.S. nonqualified pension plans are not included here because they are not protected from our creditors and therefore cannot be reflected as a reduction from our obligations under the pension plans. As a result, the reconciliation of funded status does not reflect the effect of plan assets that exist for all of our defined benefit plans. See Note 20 for the assets associated with certain U.S. nonqualified pension plans.

The actuarial loss for the year ended December 31, 2020 primarily resulted from a decrease in the discount rates used to determine our benefit obligations for our pension plans from 3.14 percent in 2019 to 2.62 percent in 2020. The actuarial loss for the year ended December 31, 2019 primarily resulted from a decrease in the discount rates used to determine our benefit obligations for our pension plans from 4.25 percent in 2018 to 3.14 percent in 2019.


	Pension Plans				Other Postretirement Benefit Plans
	December 31,				December 31,
	2020		2019		2020		2019
Deferred charges and other assets, net	$	7	$	5	$	—	$	—
Accrued expenses	(24)		(17)		(21)		(20)
Other long-term liabilities	(541)		(518)		(337)		(316)
	$	(558)	$	(530)	$	(358)	$	(336)


	Pension Plans						Other Postretirement Benefit Plans
	Year Ended December 31,						Year Ended December 31,
	2020		2019		2018		2020		2019		2018
Service cost	$	140	$	119	$	133	$	6	$	5	$	6
Interest cost	85		98		91		9		11		10
Expected return on plan assets	(179)		(166)		(163)		—		—		—
Amortization of:
Net actuarial (gain) loss	74		41		65		—		(3)		(2)
Prior service credit	(19)		(19)		(18)		(7)		(9)		(11)
Special charges	5		4		7		—		1		—
Net periodic benefit cost	$	106	$	77	$	115	$	8	$	5	$	3

Amortization of prior service credit shown in the preceding table was based on a straight-line amortization of the cost over the average remaining service period of employees expected to receive benefits under each respective plan. Amortization of the net actuarial (gain) loss shown in the preceding table was based on the straight-line amortization of the excess of the unrecognized (gain) loss over 10 percent of the greater of the projected benefit obligation or market-related value of plan assets (smoothed asset value) over the average remaining service period of active employees expected to receive benefits under each respective plan.


	Pension Plans						Other Postretirement Benefit Plans
	Year Ended December 31,						Year Ended December 31,
	2020		2019		2018		2020		2019		2018
Net gain (loss) arising during the year:
Net actuarial gain (loss)	$	(105)	$	(204)	$	(8)	$	(23)	$	(41)	$	9
Prior service (cost) credit	(5)		—		7		—		(3)		—

Net (gain) loss reclassified into income:
Net actuarial (gain) loss	74		41		65		—		(3)		(2)
Prior service credit	(19)		(19)		(18)		(7)		(9)		(11)
Curtailment and settlement loss	5		4		7		—		—		—

Total changes in other comprehensive income (loss)	$	(50)	$	(178)	$	53	$	(30)	$	(56)	$	(4)


	Pension Plans				Other Postretirement Benefit Plans
	December 31,				December 31,
	2020		2019		2020		2019
Discount rate	2.62	%	3.14	%	2.64	%	3.32	%
Rate of compensation increase	3.66	%	3.75	%	n/a		n/a
Interest crediting rate for cash balance plans	3.03	%	3.03	%	n/a		n/a

The discount rate assumption used to determine the benefit obligations as of December 31, 2020 and 2019 for the majority of our pension plans and other postretirement benefit plans was based on the Aon AA Only Above Median yield curve and considered the timing of the projected cash outflows under our

plans. This curve was designed by Aon, our actuarial consultant, to provide a means for plan sponsors to value the liabilities of their pension plans or postretirement benefit plans. To develop this curve, a hypothetical double-A yield curve represented by a series of annualized individual discount rates with maturities from one-half year to 99 years is constructed. Each bond issue underlying the double-A yield curve is required to have an average rating of double-A when averaging all available ratings by Moody’s Investors Service, Standard & Poor’s Ratings Services, and Fitch Ratings. Only the bonds representing the 50 percent highest yielding issuances of this double-A yield curve are then included in the Aon AA Only Above Median yield curve.

We based our discount rate assumption on the Aon AA Only Above Median yield curve because we believe it is representative of the types of bonds we would use to settle our pension and other postretirement benefit plan liabilities as of those dates. We believe that the yields associated with the bonds used to develop this yield curve reflect the current level of interest rates.


	Pension Plans						Other Postretirement Benefit Plans
	Year Ended December 31,						Year Ended December 31,
	2020		2019		2018		2020		2019		2018
Discount rate	3.14	%	4.24	%	3.59	%	3.32	%	4.40	%	3.72	%
Expected long-term rate of return on plan assets	7.20	%	7.22	%	7.24	%	n/a		n/a		n/a
Rate of compensation increase	3.75	%	3.78	%	3.86	%	n/a		n/a		n/a
Interest crediting rate for cash balance plans	3.03	%	3.04	%	3.04	%	n/a		n/a		n/a


	December 31,
	2020		2019
Health care cost trend rate assumed for the next year	6.83	%	7.32	%
Rate to which the cost trend rate was assumed to decline (the ultimate trend rate)	5.00	%	5.00	%
Year that the rate reaches the ultimate trend rate	2026		2026

The following tables present the fair values of the assets of our pension plans (in millions) as of December 31, 2020 and 2019 by level of the fair value hierarchy. Assets categorized in Level 1 of the hierarchy are measured at fair value using a market approach based on unadjusted quoted prices from national securities exchanges. Assets categorized in Level 2 of the hierarchy are measured at net asset value in a market that is not active or inputs other than quoted prices that are observable. As previously noted, we do not fund or fully fund U.S. nonqualified and certain international pension plans that are not subject to funding requirements, and we do not fund our other postretirement benefit plans.


	Fair Value Hierarchy						Total as of December 31, 2020
	Level 1		Level 2		Level 3
Equity securities (a)	$	682	$	—	$	—	$	682



Mutual funds	244		—		—		244


Corporate debt instruments (a)	—		297		—		297
Government securities	85		142		—		227


Common collective trusts (b)	—		1,066		—		1,066
Pooled separate accounts (c)	—		316		—		316
Private funds	—		128		—		128
Insurance contract	—		15		—		15
Interest and dividends receivable	5		—		—		5
Cash and cash equivalents	98		—		—		98
Securities transactions payable, net	(11)		—		—		(11)
Total pension plan assets	$	1,103	$	1,964	$	—	$	3,067


	Fair Value Hierarchy						Total as of December 31, 2019
	Level 1		Level 2		Level 3
Equity securities (a)	$	831	$	1	$	—	$	832



Mutual funds	213		—		—		213


Corporate debt instruments (a)	—		293		—		293
Government securities	53		148		—		201


Common collective trusts (b)	—		751		—		751
Pooled separate accounts (c)	—		250		—		250
Private funds	—		104		—		104
Insurance contract	—		17		—		17
Interest and dividends receivable	5		—		—		5
Cash and cash equivalents	59		—		—		59
Securities transactions payable, net	(16)		—		—		(16)
Total pension plan assets	$	1,145	$	1,564	$	—	$	2,709

(b)This class primarily includes investments in approximately 80 percent equities and 20 percent bonds as of December 31, 2020. As of December 31, 2019, this class included primarily investments in approximately 75 percent equities and 25 percent bonds.

The investment policies and strategies for the assets of our pension plans incorporate a well-diversified approach that is expected to earn long-term returns from capital appreciation and a growing stream of current income. This approach recognizes that assets are exposed to risk and the market value of the pension plans’ assets may fluctuate from year to year. Risk tolerance is determined based on our financial ability to withstand risk within the investment program and the willingness to accept return volatility. In line with the investment return objective and risk parameters, the pension plans’ mix of assets includes a diversified portfolio of equity and fixed-income investments. Equity securities include international stocks and a blend of U.S. growth and value stocks of various sizes of capitalization. Fixed income securities include bonds and notes issued by the U.S. government and its agencies, corporate bonds, and mortgage-backed securities. The aggregate asset allocation is reviewed on an annual basis. As of December 31, 2020, the target allocations for plan assets under our primary pension plan are 70 percent equity securities and 30 percent fixed income investments.

The expected long-term rate of return on plan assets is based on a forward-looking expected asset return model. This model derives an expected rate of return based on the target asset allocation of a plan’s assets. The underlying assumptions regarding expected rates of return for each asset class reflect Aon’s best expectations for these asset classes. The model reflects the positive effect of periodic rebalancing among diversified asset classes. We select an expected asset return that is supported by this model.

We have defined contribution plans that cover most of our employees. Our contributions to these plans are based on employees’ compensation and/or a partial match of employee contributions to the plans. Our contributions to these defined contribution plans were $80 million, $77 million, and $74 million for the years ended December 31, 2020, 2019, and 2018, respectively.