Investment Securities (Details 2) $ in Millions	Dec. 31, 2018 USD ($) securities	Dec. 31, 2017 USD ($) securities
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions [Abstract]
Number of securities, less than 12 months | securities	2	34
Number of securities, 12 months or more | securities	29	13
Number of securities, total | securities	31	47
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Estimated Fair Value, Less than 12 months	$ 224	$ 807
Estimated Fair Value, 12 months or more	873	211
Estimated Fair Value, Total	1,097	1,018
Available For Sale Securities Continuous Unrealized Aggregate Losses [Abstract]
Gross Unrealized Losses, Less than 12 months	(2)	(6)
Gross Unrealized Losses, 12 months or more	(16)	(8)
Gross Unrealized Losses, Total	$ (18)	$ (14)
Ratio Of Fair Value To Amortized Cost Between Ninety And One Hundred Percent [Member]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions [Abstract]
Number of securities, less than 12 months | securities	2	34
Number of securities, 12 months or more | securities	29	13
Number of securities, total | securities	31	47
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Estimated Fair Value, Less than 12 months	$ 224	$ 807
Estimated Fair Value, 12 months or more	873	211
Estimated Fair Value, Total	1,097	1,018
Available For Sale Securities Continuous Unrealized Aggregate Losses [Abstract]
Gross Unrealized Losses, Less than 12 months	(2)	(6)
Gross Unrealized Losses, 12 months or more	(16)	(8)
Gross Unrealized Losses, Total	$ (18)	$ (14)