Consolidated Statement of Shareholder's Interest - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Shareholder's Interest [Roll Forward]
Balance at beginning of period	$ 14,975	$ 15,884
Net income	603	701
Other Comprehensive Income (Loss), Net of Tax	20	113
Distributions declared	(675)	(1,013)
Balance at end of period	14,923	15,685
Shareholder's Interest [Member]
Shareholder's Interest [Roll Forward]
Balance at beginning of period	5,227	5,227
Net income	0	0
Other Comprehensive Income (Loss), Net of Tax	0	0
Distributions declared	0	0
Balance at end of period	5,227	5,227
Accumulated Other Comprehensive Income/(Loss) (Note11) [Member]
Shareholder's Interest [Roll Forward]
Balance at beginning of period	(829)	(419)
Net income	0	0
Other Comprehensive Income (Loss), Net of Tax	20	113
Distributions declared	0	0
Balance at end of period	(809)	(306)
Retained Earnings [Member]
Shareholder's Interest [Roll Forward]
Balance at beginning of period	10,577	11,076
Net income	603	701
Other Comprehensive Income (Loss), Net of Tax	0	0
Distributions declared	(675)	(1,013)
Balance at end of period	$ 10,505	$ 10,764