Temporarily Impaired Securities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 516		$ 134
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(88)		(6)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	34		75
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(29)		(15)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	550		209
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(117)		(21)
Equity Securities, Net Unrealized Gain (Loss)	1	$ 5
Equity securities 3	8		15
Equity Securities without Readily Determinable Fair Value, Amount	190		189
US Treasury and Government [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	109		55
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(22)		(3)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	10		23
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(11)		(8)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	119		78
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(33)		(11)
Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	407		79
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(66)		(3)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	24		52
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(18)		(7)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	431		131
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (84)		$ (10)