Investments (Continuous Gross Unrealized Losses for Fixed Maturity Securities Available-For-Sale) (Details) $ in Millions	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Debt Securities, Available-for-sale [Line Items]
Total number of securities in an unrealized loss position less than 12 months	6,913	2,598
Total number of securities in an unrealized loss position equal to or greater than 12 months	2,335	1,955
Fixed Maturity Securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 months Estimated Fair Value	$ 83,208	$ 41,943
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3,565	435
Equal to or Greater than 12 Months Estimated Fair Value	31,301	23,375
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2,390	1,468
U.S. corporate
Debt Securities, Available-for-sale [Line Items]
Less than 12 months Estimated Fair Value	32,430	5,604
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,663	92
Equal to or Greater than 12 Months Estimated Fair Value	5,826	4,115
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	617	259
Debt Security, Government, Non-US [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months Estimated Fair Value	4,392	4,234
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	243	83
Equal to or Greater than 12 Months Estimated Fair Value	2,902	3,251
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	228	229
Foreign corporate
Debt Securities, Available-for-sale [Line Items]
Less than 12 months Estimated Fair Value	19,564	4,422
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,230	99
Equal to or Greater than 12 Months Estimated Fair Value	5,765	6,802
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	795	577
U.S. government and agency
Debt Securities, Available-for-sale [Line Items]
Less than 12 months Estimated Fair Value	6,813	18,273
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	58	93
Equal to or Greater than 12 Months Estimated Fair Value	8,937	3,560
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	406	186
Residential Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months Estimated Fair Value	6,506	6,359
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	120	50
Equal to or Greater than 12 Months Estimated Fair Value	6,423	4,159
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	248	141
ABS
Debt Securities, Available-for-sale [Line Items]
Less than 12 months Estimated Fair Value	8,230	1,695
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	138	7
Equal to or Greater than 12 Months Estimated Fair Value	392	729
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	16	31
Municipals
Debt Securities, Available-for-sale [Line Items]
Less than 12 months Estimated Fair Value	1,380	182
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	46	2
Equal to or Greater than 12 Months Estimated Fair Value	349	346
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	25	12
CMBS
Debt Securities, Available-for-sale [Line Items]
Less than 12 months Estimated Fair Value	3,893	1,174
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	67	9
Equal to or Greater than 12 Months Estimated Fair Value	707	413
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 55	$ 33