Employee Benefit Plans - Fair Value Measurements (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018	Dec. 31, 2017
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss)		$ 40		$ 122
Defined Benefit Plan, Plan Assets, Payment for Settlement		0		0
Defined Benefit Plan, Plan Assets, Amount		744		742		$ 664
Other Postretirement Benefits Plan [Member] | Limited Partnership Interests [Member] | Fair Value Measured at Net Asset Value Per Share [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		4		5
Other Postretirement Benefits Plan [Member] | Defined Benefit Plan, Assets Before Investment Funds, Partnership Interests And Real Estate Funds | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		573		568
Other Postretirement Benefits Plan [Member] | Defined Benefit Plan, Assets Before Investment Funds, Partnership Interests And Real Estate Funds | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		340		433
Other Postretirement Benefits Plan [Member] | Defined Benefit Plan, Assets Before Investment Funds, Partnership Interests And Real Estate Funds | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		233		135
Other Postretirement Benefits Plan [Member] | Defined Benefit Plan, Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		22		18
Other Postretirement Benefits Plan [Member] | Defined Benefit Plan, Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		20		17	[1]
Other Postretirement Benefits Plan [Member] | Defined Benefit Plan, Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		2		1	[1]
Other Postretirement Benefits Plan [Member] | US Treasury Securities [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		15		23
Other Postretirement Benefits Plan [Member] | US Treasury Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		15		23
Other Postretirement Benefits Plan [Member] | US Treasury Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		0		0
Other Postretirement Benefits Plan [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		102		44
Other Postretirement Benefits Plan [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		0		0
Other Postretirement Benefits Plan [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		102		44
Other Postretirement Benefits Plan [Member] | Municipal Bonds [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		82		57
Other Postretirement Benefits Plan [Member] | Municipal Bonds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		0		0
Other Postretirement Benefits Plan [Member] | Municipal Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		82		57
Other Postretirement Benefits Plan [Member] | Agency, Asset and Mortgage-Backed Securities | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		47		33
Other Postretirement Benefits Plan [Member] | Agency, Asset and Mortgage-Backed Securities | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		0		0
Other Postretirement Benefits Plan [Member] | Agency, Asset and Mortgage-Backed Securities | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		47		33
Other Postretirement Benefits Plan [Member] | Domestic Equity Securities [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		6		151
Other Postretirement Benefits Plan [Member] | Domestic Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		6		151	[1]
Other Postretirement Benefits Plan [Member] | Domestic Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		$ 0		0	[1]
Other Postretirement Benefits Plan [Member] | Foreign Equity Securities [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount				6
Other Postretirement Benefits Plan [Member] | Foreign Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	[1]			6
Other Postretirement Benefits Plan [Member] | Foreign Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount				$ 0
Other Postretirement Benefits Plan [Member] | Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of Investment Funds Comprised of Equity Securitites		40.00%		58.00%
Percentage of Investment Funds Comprised of Debt Securities		60.00%		42.00%
Percentage of Investment Funds Invested in United States Securities		79.00%		75.00%
Percentage of Investment Funds Invested in International Securities		21.00%		25.00%
Other Postretirement Benefits Plan [Member] | Equity Funds [Member] | Fair Value Measured at Net Asset Value Per Share [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		$ 167		$ 169	[2]
Other Postretirement Benefits Plan [Member] | Defined Benefit Plan, Equity Securities | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		299		236
Other Postretirement Benefits Plan [Member] | Defined Benefit Plan, Equity Securities | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		299		236
Other Postretirement Benefits Plan [Member] | Defined Benefit Plan, Equity Securities | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		0		0
UNITED STATES | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss)		373		456
Defined Benefit Plan, Plan Assets, Payment for Settlement		0		(22)
Defined Benefit Plan, Plan Assets, Amount		2,824		2,656		2,396
UNITED STATES | Pension Plan [Member] | Limited Partnership Interests [Member] | Fair Value Measured at Net Asset Value Per Share [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		88		93	[3]
UNITED STATES | Pension Plan [Member] | Real Estate Funds [Member] | Fair Value Measured at Net Asset Value Per Share [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		43		42
UNITED STATES | Pension Plan [Member] | Defined Benefit Plan, Assets Before Investment Funds, Partnership Interests And Real Estate Funds | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		1,172		1,606
UNITED STATES | Pension Plan [Member] | Defined Benefit Plan, Assets Before Investment Funds, Partnership Interests And Real Estate Funds | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		276		1,045
UNITED STATES | Pension Plan [Member] | Defined Benefit Plan, Assets Before Investment Funds, Partnership Interests And Real Estate Funds | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		896		561	[4]
UNITED STATES | Pension Plan [Member] | Defined Benefit Plan, Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		79		63
UNITED STATES | Pension Plan [Member] | Defined Benefit Plan, Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		0		27
UNITED STATES | Pension Plan [Member] | Defined Benefit Plan, Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		79		36
UNITED STATES | Pension Plan [Member] | US Treasury Securities [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		52		210
UNITED STATES | Pension Plan [Member] | US Treasury Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		52		210
UNITED STATES | Pension Plan [Member] | US Treasury Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		0		0	[4]
UNITED STATES | Pension Plan [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		748		376
UNITED STATES | Pension Plan [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		0		0	[4]
UNITED STATES | Pension Plan [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		748		376	[4]
UNITED STATES | Pension Plan [Member] | Municipal Bonds [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		69		28
UNITED STATES | Pension Plan [Member] | Municipal Bonds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		0		0	[4]
UNITED STATES | Pension Plan [Member] | Municipal Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		69		28
UNITED STATES | Pension Plan [Member] | Domestic Equity Securities [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		224		548
UNITED STATES | Pension Plan [Member] | Domestic Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		224		547	[4]
UNITED STATES | Pension Plan [Member] | Domestic Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		$ 0		1	[4]
UNITED STATES | Pension Plan [Member] | Debt Security, Government, Non-US [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount				5
UNITED STATES | Pension Plan [Member] | Debt Security, Government, Non-US [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount				0
UNITED STATES | Pension Plan [Member] | Debt Security, Government, Non-US [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	[4]			5
UNITED STATES | Pension Plan [Member] | US Government-sponsored Enterprises Debt Securities [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount				115
UNITED STATES | Pension Plan [Member] | US Government-sponsored Enterprises Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount				0
UNITED STATES | Pension Plan [Member] | US Government-sponsored Enterprises Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount				115
UNITED STATES | Pension Plan [Member] | Foreign Equity Securities [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount				136
UNITED STATES | Pension Plan [Member] | Foreign Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount				136
UNITED STATES | Pension Plan [Member] | Foreign Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	[4]			$ 0
UNITED STATES | Pension Plan [Member] | Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of Investment Funds Comprised of Equity Securitites		69.00%		62.00%
Percentage of Investment Funds Comprised of Debt Securities		31.00%		38.00%
Percentage of Investment Funds Invested in United States Securities		79.00%		66.00%
Percentage of Investment Funds Invested in International Securities		21.00%		34.00%
UNITED STATES | Pension Plan [Member] | Equity Funds [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	[5]			$ 125
UNITED STATES | Pension Plan [Member] | Equity Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	[4],[5]			125
UNITED STATES | Pension Plan [Member] | Equity Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount				0
UNITED STATES | Pension Plan [Member] | Equity Funds [Member] | Fair Value Measured at Net Asset Value Per Share [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		$ 1,521		915	[5]
UNITED KINGDOM | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss)		181		194
Defined Benefit Plan, Plan Assets, Payment for Settlement		(63)		(99)
Defined Benefit Plan, Plan Assets, Amount		2,334		2,151		1,989
Defined Benefit Plan, Plan Assets, Foreign Currency Translation Gain (Loss)		75		81
UNITED KINGDOM | Pension Plan [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		2,226		2,048
UNITED KINGDOM | Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	[6]	1,107		963
UNITED KINGDOM | Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		882		842
UNITED KINGDOM | Pension Plan [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	[6]	237		243
UNITED KINGDOM | Pension Plan [Member] | United Kingdom Government Obligations [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		1,102		960
UNITED KINGDOM | Pension Plan [Member] | United Kingdom Government Obligations [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		1,102		960
UNITED KINGDOM | Pension Plan [Member] | United Kingdom Government Obligations [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		0	[6]	0
UNITED KINGDOM | Pension Plan [Member] | United Kingdom Government Obligations [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		0		0
UNITED KINGDOM | Pension Plan [Member] | Real Estate Funds [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		237		243
UNITED KINGDOM | Pension Plan [Member] | Real Estate Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		0		0
UNITED KINGDOM | Pension Plan [Member] | Real Estate Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		0		0
UNITED KINGDOM | Pension Plan [Member] | Real Estate Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		237	[6]	243	[6]	239	$ 230
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held		(13)		(5)		23
Defined Benefit Plan, Plan Assets, Foreign Currency Translation Gain (Loss)		7		9		$ (14)
UNITED KINGDOM | Pension Plan [Member] | Cash Equivalents [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		54		27
UNITED KINGDOM | Pension Plan [Member] | Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		5		3	[6]
UNITED KINGDOM | Pension Plan [Member] | Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	[6]	49		24
UNITED KINGDOM | Pension Plan [Member] | Cash Equivalents [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	[6]	$ 0		$ 0
UNITED KINGDOM | Pension Plan [Member] | Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of Investment Funds Comprised of Equity Securitites		40.00%		38.00%
Percentage of Investment Funds Comprised of Debt Securities		60.00%		62.00%
UNITED KINGDOM | Pension Plan [Member] | Equity Funds [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	[7]	$ 833		$ 818
UNITED KINGDOM | Pension Plan [Member] | Equity Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	[6],[7]	0		0
UNITED KINGDOM | Pension Plan [Member] | Equity Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		833		818
UNITED KINGDOM | Pension Plan [Member] | Equity Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		0		0	[6],[7]
UNITED KINGDOM | Pension Plan [Member] | Equity Funds [Member] | Fair Value Measured at Net Asset Value Per Share [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	[7]	$ 108		$ 103

[1] Refer to Note 15 for additional discussion regarding the three levels of the fair value hierarchy.

[2] Investment funds are comprised of mutual funds and collective trust funds. These funds consist of equity and debt securities of approximately 40% and 60%, respectively, for 2020 and 58% and 42%, respectively, for 2019. Additionally, these funds are invested in United States and international securities of approximately 79% and 21%, respectively, for 2020 and 75% and 25%, respectively, for 2019.

[3] Limited partnership interests include several funds that invest primarily in real estate, buyout, growth equity and venture capital.

[4] Refer to Note 15 for additional discussion regarding the three levels of the fair value hierarchy.

[5] Investment funds are comprised of mutual funds and collective trust funds. These funds consist of equity and debt securities of approximately 69% and 31%, respectively, for 2020 and 62% and 38%, respectively, for 2019. Additionally, these funds are invested in United States and international securities of approximately 79% and 21%, respectively, for 2020 and 66% and 34%, respectively, for 2019.

[6] Refer to Note 15 for additional discussion regarding the three levels of the fair value hierarchy.

[7] Investment funds are comprised of mutual funds and collective trust funds. These funds consist of equity and debt securities of approximately 40% and 60%, respectively, for 2020 and 38% and 62%, respectively, for 2019.