Employee Benefit Plans (Significant Unobservable Inputs) (Details) - Pension Benefits - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	$ 8,751	$ 9,003
Purchases, sales, issuances and settlements, net	(7)	(3)
Estimated fair value of plan assets at December 31,	9,164	8,751
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,	3,057
Estimated fair value of plan assets at December 31,	3,552	3,057
Foreign government
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	781
Estimated fair value of plan assets at December 31,	876	781
Other (1)
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	419
Estimated fair value of plan assets at December 31,	376	419
Other investments
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	839
Estimated fair value of plan assets at December 31,	772	839
Derivative assets
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward]
Estimated fair value of plan assets at January 1,	105
Estimated fair value of plan assets at December 31,	78	105
Level 3
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,	711	901
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,	78	80
Realized gains (losses)	2	1
Unrealized gains (losses)	3	(4)
Purchases, sales, issuances and settlements, net	(21)	8
Transfers into and/or out of Level 3	(62)	(7)
Estimated fair value of plan assets at December 31,	0	78
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,	17	17
Realized gains (losses)	0	0
Unrealized gains (losses)	(3)	(1)
Purchases, sales, issuances and settlements, net	(3)	2
Transfers into and/or out of Level 3	(11)	(1)
Estimated fair value of plan assets at December 31,	0	17
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,	7	8
Realized gains (losses)	0	0
Unrealized gains (losses)	0	2
Purchases, sales, issuances and settlements, net	0	(1)
Transfers into and/or out of Level 3	2	(2)
Estimated fair value of plan assets at December 31,	9	7
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,	723	745
Realized gains (losses)	0	0
Unrealized gains (losses)	33	55
Purchases, sales, issuances and settlements, net	(119)	(77)
Transfers into and/or out of Level 3	0	0
Estimated fair value of plan assets at December 31,	637	723
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,	76	73
Realized gains (losses)	3	(11)
Unrealized gains (losses)	(18)	(9)
Purchases, sales, issuances and settlements, net	6	23
Transfers into and/or out of Level 3	(2)	0
Estimated fair value of plan assets at December 31,	$ 65	$ 76