Employee Benefit Plans (Significant Unobservable Inputs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	$ 8,948	$ 9,688
Purchases, sales, issuances and settlements, net	(5)	(5)
Estimated fair value of plan assets at December 31,	10,230	8,948
Pension Benefits | Corporate fixed maturity securities
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	3,351
Estimated fair value of plan assets at December 31,	3,750	3,351
Pension Benefits | Foreign government
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	837
Estimated fair value of plan assets at December 31,	996	837
Pension Benefits | Other (1)
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	801
Estimated fair value of plan assets at December 31,	948	801
Pension Benefits | Equity securities
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	901
Estimated fair value of plan assets at December 31,	1,177	901
Pension Benefits | Other investments
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	708
Estimated fair value of plan assets at December 31,	712	708
Pension Benefits | Derivative assets
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	38
Estimated fair value of plan assets at December 31,	13	38
Other Postretirement Benefits
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	1,360	1,434
Purchases, sales, issuances and settlements, net	(3)	16
Estimated fair value of plan assets at December 31,	1,468	1,360
Other Postretirement Benefits | Corporate fixed maturity securities
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	313
Estimated fair value of plan assets at December 31,	278	313
Other Postretirement Benefits | Foreign government
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	90
Estimated fair value of plan assets at December 31,	63	90
Other Postretirement Benefits | Other (1)
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	72
Estimated fair value of plan assets at December 31,	373	72
Other Postretirement Benefits | Equity securities
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	173
Estimated fair value of plan assets at December 31,	59	173
Other Postretirement Benefits | Other investments
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	0
Estimated fair value of plan assets at December 31,	0	0
Other Postretirement Benefits | Derivative assets
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	1
Estimated fair value of plan assets at December 31,	0	1
Level 3 | Pension Benefits
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	691
Estimated fair value of plan assets at December 31,	686	691
Level 3 | Pension Benefits | Corporate fixed maturity securities
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	1	1
Realized gains (losses)	0	0
Unrealized gains (losses)	0	0
Purchases, sales, issuances and settlements, net	(1)	0
Transfers into and/or out of Level 3	0	0
Estimated fair value of plan assets at December 31,	0	1
Level 3 | Pension Benefits | Foreign government
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	0
Estimated fair value of plan assets at December 31,	0	0
Level 3 | Pension Benefits | Other (1)
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	1	10
Realized gains (losses)	0	0
Unrealized gains (losses)	0	0
Purchases, sales, issuances and settlements, net	2	(3)
Transfers into and/or out of Level 3	0	(6)
Estimated fair value of plan assets at December 31,	0	1
Level 3 | Pension Benefits | Equity securities
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	0	3
Realized gains (losses)	0	0
Unrealized gains (losses)	0	0
Purchases, sales, issuances and settlements, net	0	0
Transfers into and/or out of Level 3	0	(3)
Estimated fair value of plan assets at December 31,	0	0
Level 3 | Pension Benefits | Other investments
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	688	622
Realized gains (losses)	0	0
Unrealized gains (losses)	(1)	23
Purchases, sales, issuances and settlements, net	(1)	43
Transfers into and/or out of Level 3	0	0
Estimated fair value of plan assets at December 31,	686	688
Level 3 | Pension Benefits | Derivative assets
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	1	0
Realized gains (losses)	0	0
Unrealized gains (losses)	(1)	0
Purchases, sales, issuances and settlements, net	0	0
Transfers into and/or out of Level 3	0	1
Estimated fair value of plan assets at December 31,	0	1
Level 3 | Other Postretirement Benefits
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	0
Estimated fair value of plan assets at December 31,	3	0
Level 3 | Other Postretirement Benefits | Corporate fixed maturity securities
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	0
Estimated fair value of plan assets at December 31,	0	0
Level 3 | Other Postretirement Benefits | Foreign government
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	0
Estimated fair value of plan assets at December 31,	0	0
Level 3 | Other Postretirement Benefits | Other (1)
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	0
Estimated fair value of plan assets at December 31,	3	0
Level 3 | Other Postretirement Benefits | Equity securities
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	0
Estimated fair value of plan assets at December 31,	0	0
Level 3 | Other Postretirement Benefits | Other investments
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	0
Estimated fair value of plan assets at December 31,	0	0
Level 3 | Other Postretirement Benefits | Derivative assets
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	0
Estimated fair value of plan assets at December 31,	$ 0	$ 0