Retirement Plans Retirement Plans (Fair Value, Investments, Entities That Calculate Net Asset Value Per Share) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	$ 419	$ 383
Investments, Fair Value Disclosure	3,535	4,386
Equity Securities, US [Member]
Defined Benefit Plan Disclosure [Line Items]
Alternative Investment	515	708
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	$ 0	$ 0
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Frequency	Daily to monthly	Daily to monthly
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Description	1-5 days	1-5 days
Equity Securities, Non-US [Member]
Defined Benefit Plan Disclosure [Line Items]
Alternative Investment	$ 433	$ 866
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	$ 0	$ 0
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Frequency	Daily to monthly	Daily to monthly
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Description	1-5 days	1-5 days
Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Alternative Investment	$ 59	$ 66
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	$ 0	$ 0
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Frequency	Daily to monthly	Daily to monthly
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Description	1-5 days	1-5 days
Other Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Alternative Investment	$ 180	$ 232
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	$ 0	$ 0
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Frequency	Daily to monthly	Daily to monthly
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Description	1-5 days	1-5 days
Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Alternative Investment	$ 944	$ 1,106
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	$ 109	$ 121
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Frequency	Quarterly	Quarterly
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Description	45 - 60 days	45 - 60 days
Private Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Alternative Investment	$ 518	$ 481
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	$ 310	$ 262
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Frequency	(a)	(a)
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Description	None	None
Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Alternative Investment	$ 886	$ 927
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	$ 0	$ 0
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Frequency	Daily to annually	Daily to annually
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Description	1 - 100 days	1 - 100 days

Fair value of investment other than investment in equity security, investment in debt security and equity method investment. Includes, but is not limited to, investment in certain entities that calculate net asset value per share. Example includes, but is not limited to, investment in hedge fund, venture capital fund, private equity fund, and real estate partnership or fund.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 6A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=SL6742756-110258

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 35
-Paragraph 54B
-URI http://asc.fasb.org/extlink&oid=99392525&loc=SL7495116-110257

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- Definition

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- Definition

Describes the terms and conditions for redemption of the entity's investment, or portion thereof (for example, quarterly redemption with 60 days notice), for each of those certain investments for which net asset value per share is calculated (including by unit, membership interest, or other equity (ownership interest) unit measure) (alternative investments), by major category.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 6A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=SL6742756-110258

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States the frequency (for example, annually, semi-annually, quarterly) with which the entity can redeem its investment, or portion thereof, for each of those certain investments for which net asset value per share is calculated (including by unit, membership interest, or other equity (ownership interest) unit measure) (alternative investments), by major category.

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The amount of unfunded commitments for which the entity is obligated, to those certain investments for which net asset value per share is calculated (including by unit, membership interest, or other equity (ownership interest) unit measure) (alternative investments).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 6A
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=SL6742756-110258

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

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