Income Taxes - Income from continuing operations before income tax (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income before income taxes:
Income from continuing operations before income taxes	$ 1,689	$ 1,765	$ 1,538
Current:
Total current	490	468	404
Deferred tax expense (benefit):
Total deferred	(223)	(134)	(14)
Total income taxes expenses	267	334	390
U.K. [Member]
Income before income taxes:
Income from continuing operations before income taxes	149	347	96
Current:
Total current	43	1	(18)
Deferred tax expense (benefit):
Total deferred	(39)	38	43
U.S. [Member]
Income before income taxes:
Income from continuing operations before income taxes	(51)	(55)	349
Current:
Total current	137	156	111
Deferred tax expense (benefit):
Total deferred	(140)	(133)	(48)
U.S. state and local [Member]
Current:
Total current	54	75	52
Deferred tax expense (benefit):
Total deferred	(14)	(24)	10
Other [Member]
Income before income taxes:
Income from continuing operations before income taxes	1,591	1,473	1,093
Current:
Total current	256	236	259
Deferred tax expense (benefit):
Total deferred	$ (30)	$ (15)	$ (19)