Investments (Fixed Maturity Securities Available-For-Sale by Sector) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	$ 286,816	$ 286,069
Gross Unrealized OTTI Loss	(25)	(41)	$ (8)
Debt Securities, Available-for-sale	298,265	308,931
Debt Securities [Member]
Debt Securities, Available-for-sale [Abstract]
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	17,404	24,765
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	5,980	1,945
Gross Unrealized OTTI Loss	(25)	(42)
Debt Security, Corporate, US [Member]
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	77,761	76,005
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	3,467	7,007
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	2,280	351
Gross Unrealized OTTI Loss	0	0
Debt Securities, Available-for-sale	78,948	82,661
Debt Security, Government, Non-US [Member]
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	56,353	55,351
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	6,406	6,495
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	471	312
Gross Unrealized OTTI Loss	0	0
Debt Securities, Available-for-sale	62,288	61,534
Debt Security, Corporate, Non-US [Member]
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	56,290	52,409
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	2,438	3,836
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	2,025	676
Gross Unrealized OTTI Loss	0	0
Debt Securities, Available-for-sale	56,703	55,569
US Treasury and Government [Member]
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	37,030	43,446
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	2,756	4,227
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	464	279
Gross Unrealized OTTI Loss	0	0
Debt Securities, Available-for-sale	39,322	47,394
Residential Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	27,409	27,846
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	920	1,145
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	394	233
Gross Unrealized OTTI Loss	(26)	(42)
Debt Securities, Available-for-sale	27,961	28,800
Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	12,552	12,213
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	74	116
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	153	39
Gross Unrealized OTTI Loss	(1)	1
Debt Securities, Available-for-sale	12,472	12,291
Municipals
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	10,376	10,752
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	1,228	1,717
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	71	13
Gross Unrealized OTTI Loss	0	1
Debt Securities, Available-for-sale	11,533	12,455
Commercial Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	9,045	8,047
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	115	222
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	122	42
Gross Unrealized OTTI Loss	0	0
Debt Securities, Available-for-sale	$ 9,038	$ 8,227