Employee Benefit Plans (Significant Unobservable Inputs) (Details) - Pension Benefits - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	$ 9,009	$ 8,603
Purchases, sales, issuances and settlements, net	(30)	(7)
Estimated fair value of plan assets at December 31,	9,688	9,009
Corporate fixed maturity securities [Member]
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	3,499
Estimated fair value of plan assets at December 31,	3,834	3,499
Foreign government
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	862
Estimated fair value of plan assets at December 31,	1,037	862
Other (1)
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	371
Estimated fair value of plan assets at December 31,	405	371
Common Stock - Foreign
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	449
Estimated fair value of plan assets at December 31,	407	449
Other investments
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	772
Estimated fair value of plan assets at December 31,	785	772
Derivative assets
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	78
Estimated fair value of plan assets at December 31,	35	78
Level 3
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	711
Estimated fair value of plan assets at December 31,	636	711
Level 3 | Corporate fixed maturity securities [Member]
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	0	77
Realized gains (losses)	(10)	2
Unrealized gains (losses)	10	3
Purchases, sales, issuances and settlements, net	0	(20)
Transfers into and/or out of Level 3	1	(62)
Estimated fair value of plan assets at December 31,	1	0
Level 3 | Foreign government
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	0	17
Realized gains (losses)	0	0
Unrealized gains (losses)	0	(3)
Purchases, sales, issuances and settlements, net	0	(3)
Transfers into and/or out of Level 3	0	(11)
Estimated fair value of plan assets at December 31,	0	0
Level 3 | Other (1)
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	9	7
Realized gains (losses)	0	0
Unrealized gains (losses)	0	0
Purchases, sales, issuances and settlements, net	8	0
Transfers into and/or out of Level 3	(7)	2
Estimated fair value of plan assets at December 31,	10	9
Level 3 | Common Stock - Foreign
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	0	0
Realized gains (losses)	2	0
Unrealized gains (losses)	0	0
Purchases, sales, issuances and settlements, net	(4)	0
Transfers into and/or out of Level 3	5	0
Estimated fair value of plan assets at December 31,	3	0
Level 3 | Other investments
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	637	723
Realized gains (losses)	0	0
Unrealized gains (losses)	(12)	33
Purchases, sales, issuances and settlements, net	0	(119)
Transfers into and/or out of Level 3	(3)	0
Estimated fair value of plan assets at December 31,	622	637
Level 3 | Derivative assets
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	65	76
Realized gains (losses)	(22)	3
Unrealized gains (losses)	6	(18)
Purchases, sales, issuances and settlements, net	(48)	6
Transfers into and/or out of Level 3	(1)	(2)
Estimated fair value of plan assets at December 31,	$ 0	$ 65