Consolidated Statement of Shareholder's Interest - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Shareholder's Interest [Roll Forward]
Balance at beginning of period			$ 5,227				$ 5,227
Net income	$ 571	$ 613	603	$ 518	$ 479	$ 701	1,787	$ 1,698
Other Comprehensive Income (Loss), Net of Tax	(210)	8	20	(49)	(364)	113
Distributions declared	(1,100)	(650)	(675)	(600)	(450)	(1,013)
Balance at end of period	5,227						5,227
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	14,155	14,894	14,923	15,219	15,350	15,685	14,155	15,219
Shareholder's Interest [Member]
Shareholder's Interest [Roll Forward]
Balance at beginning of period	5,227	5,227	5,227	5,227	5,227	5,227	5,227	5,227
Net income	0	0	0	0	0	0
Other Comprehensive Income (Loss), Net of Tax	0	0	0	0	0	0
Distributions declared	0	0	0	0	0	0
Balance at end of period	5,227	5,227	5,227	5,227	5,227	5,227	5,227	5,227
Accumulated Other Comprehensive Income/(Loss) (Note11) [Member]
Shareholder's Interest [Roll Forward]
Balance at beginning of period	(801)	(809)	(829)	(670)	(306)	(419)	(829)	(419)
Net income	0	0	0	0	0	0
Other Comprehensive Income (Loss), Net of Tax	(210)	8	20	(49)	(364)	113
Distributions declared	0	0	0	0	0	0
Balance at end of period	(1,011)	(801)	(809)	(719)	(670)	(306)	(1,011)	(719)
Retained Earnings [Member]
Shareholder's Interest [Roll Forward]
Balance at beginning of period	10,468	10,505	10,577	10,793	10,764	11,076	10,577	11,076
Net income	571	613	603	518	479	701
Other Comprehensive Income (Loss), Net of Tax	0	0	0	0	0	0
Distributions declared	1,100	(650)	(675)	(600)	(450)	(1,013)
Balance at end of period	$ 9,939	$ 10,468	$ 10,505	$ 10,711	$ 10,793	$ 10,764	$ 9,939	$ 10,711